Aspects of energetic substrate metabolism of in vitro and in vivo bovine embryos

Although the metabolism of early bovine embryos has not been fully elucidated, several publications have addressed this important issue to improve culture conditions for cattle reproductive biotechnologies, with the ultimate goal of producing in vitro embryos similar in quality to those developing in vivo. Here, we review general aspects of bovine embryo metabolism in vitro and in vivo, and discuss the use of metabolic analysis of embryos produced in vitro to assess viability and predict a viable pregnancy after transference to the female tract.

Aspects of energetic substrate metabolism of in vitro and in vivo bovine embryos.

Although the metabolism of early bovine embryos has not been fully elucidated, several publications have addressed this important issue to improve culture conditions for cattle reproductive biotechnologies, with the ultimate goal of producing in vitro embryos similar in quality to those developing in vivo. Here, we review general aspects of bovine embryo metabolism in vitro and in vivo, and discuss the use of metabolic analysis of embryos produced in vitro to assess viability and predict a viable pregnancy after transference to the female tract.

Culture of bovine ovarian follicle wall sections maintained the highly estrogenic profile under basal and chemically defined conditions.

Follicle cultures reproduce in vitro the functional features observed in vivo. In a search for an ideal model, we cultured bovine antral follicle wall sections (FWS) in a serum-free defined medium (DM) known to induce 17ß-estradiol (E2) production, and in a nondefined medium (NDM) containing serum. Follicles were sectioned and cultured in NDM or DM for 24 or 48 h. Morphological features were determined by light microscopy. Gene expression of steroidogenic enzymes and follicle-stimulating hormone (FSH) receptor were determined by RT-PCR; progesterone (P4) and E2 concentrations in the media were measured by radioimmunoassay. DM, but not NDM, maintained an FWS morphology in vitro that was similar to fresh tissue. DM also induced an increase in the expression of all steroidogenic enzymes, except FSH receptor, but NDM did not. In both DM and NDM, there was a gradual increase in P4 throughout the culture period; however, P4 concentration was significantly higher in NDM. In both media, E2 concentration was increased at 24 h, followed by a decrease at 48 h. The E2:P4 ratio was higher in DM than in NDM. These results suggest that DM maintains morphological structure, upregulates the expression of steroidogenic enzyme genes, and maintains steroid production with a high E2:P4 ratio in FWS cultures.

Culture of bovine ovarian follicle wall sections maintained the highly estrogenic profile under basal and chemically defined conditions

Follicle cultures reproduce in vitro the functional features observed in vivo. In a search for an ideal model, we cultured bovine antral follicle wall sections (FWS) in a serum-free defined medium (DM) known to induce 17β-estradiol (E2) production, and in a nondefined medium (NDM) containing serum. Follicles were sectioned and cultured in NDM or DM for 24 or 48 h. Morphological features were determined by light microscopy. Gene expression of steroidogenic enzymes and follicle-stimulating hormone (FSH) receptor were determined by RT-PCR; progesterone (P4) and E2 concentrations in the media were measured by radioimmunoassay. DM, but not NDM, maintained an FWS morphology in vitro that was similar to fresh tissue. DM also induced an increase in the expression of all steroidogenic enzymes, except FSH receptor, but NDM did not. In both DM and NDM, there was a gradual increase in P4 throughout the culture period; however, P4 concentration was significantly higher in NDM. In both media, E2 concentration was increased at 24 h, followed by a decrease at 48 h. The E2:P4 ratio was higher in DM than in NDM. These results suggest that DM maintains morphological structure, upregulates the expression of steroidogenic enzyme genes, and maintains steroid production with a high E2:P4 ratio in FWS cultures.

Induction of reversible meiosis arrest of bovine oocytes using a two-step procedure under defined and nondefined conditions.

The objective was to study the effect of a defined culture system, on nuclear and cytoplasmic maturation of bovine oocytes, using the two-step procedure of IVM to detect possible inhibition and subsequent resumption of meiosis arrest. In the first step, called the prematuration period (PMP), COCs were cultured in T1-non-defined medium (NDM), or T2-defined medium (DM), both for 24 h. In step 2, called the resumption period (RP), COCs were cultured in: NDM (T1); DM + NDM (T3); or DM+DM (T4) for 24 h in each medium. The NDM was composed of TCM-199 supplemented with FCS and FSH. The DM was composed of alpha-MEM supplemented with PVA, insulin, IGF-1, androstenedione, nonessential amino acids, transferrin, and sodium selenium. Oocytes from T2 had a lower (P < 0.05) rate of nuclear maturation (19.8%) than T1 oocytes (83.2%). Also, T2 COCs appeared to be in the process of cytoplasmic maturation, according to the distribution of organelles assessed by transmission electron microscopy (MET). These COCs had characteristics previously described as mature: erect microvilli on the plasmembrane, presence of cortical/evenly distributed mitochondria throughout the ooplasm, and presence of 50% aligned/cluster cortical granules. Immature characteristics such as small PvS, compact cumulus cells, and presence of 50% cortical granule clusters were also observed. The T1 COCs had only characteristics of maturation (P < 0.05). In step 2 (RP), meiosis arrest induced by DM was resumed after an additional 24 h of culture in NDM (T3) with 79.2% mature COCs, whereas in T4, meiosis arrest was maintained, resulting in almost 70% immature COCs (P < 0.05). At the end of RP, T3 COCs had the mature characteristics of mitochondria spread throughout the cytoplasm (P < 0.05), cumulus expansion, and alignment of cortical granules, whereas the T4 group had both immature and mature characteristics. We inferred that DM can be used in lieu of meiosis inhibitors and furthermore, it can provide extra time to study nuclear and cytoplasmic maturation synchrony of IVM.

Preimplantation development and expression of Hsp-70 and Bax genes in bovine blastocysts derived from oocytes matured in alpha-MEM supplemented with growth factors and synthetic macromolecules.

In vitro culture conditions affect both the maternal and embryonic expression of genes and is likely to alter both oocyte and embryo developmental competence. The search for better and less variable culture conditions simulating those in vivo has led to the development of defined culture media, with lower impact on the molecular reprogramming of oocytes and embryos. We evaluated embryo development and relative abundance (RA) of Hsp-70 and Bax transcripts in bovine blastocysts produced from oocytes matured in a chemically defined IVM system with synthetic polymers. Immature cumulus oocyte complexes (COCs) were matured for 22-24h in alpha-MEM supplemented with IGF-1, insulin, 0.1% polyvinyl alcohol (PVA), or 0.1% polyvinylpyrrolidone (PVP), but without FSH or LH. The control group consisted of COCs matured in TCM plus FSH and 10% estrous cow serum. After fertilization, presumptive zygotes were co-cultured with cumulus cells until 224 h post-insemination. Total RNA was isolated from embryo pools, reverse transcribed into cDNA, and subjected to transcript analysis by real-time PCR. Cleavage rate was higher (P<0.05) for the control group (68.3%) than for the PVA (54.4%) and PVP-40 (58.3%) groups. Nevertheless, there was no difference among the PVA, PVP-40 and control groups in blastocyst or hatching rates. Similarly, no difference in relative abundance of Hsp-70 and Bax transcripts was detected in comparison to the control group. We inferred that bovine oocytes can be matured in serum- and gonadotrophin-free medium supplemented with PVA or PVP, enriched with IGF-I and insulin, without altering post-cleavage development and relative abundance of some genes associated with stress and apoptosis.

Prolactin and cortisol levels in women with endometriosis.

Endometriosis is a progressive estrogen-dependent disease affecting women during their reproductive years. The objective of the present study was to investigate whether endometriosis is associated with stress parameters. We determined cortisol and prolactin levels in serum, peritoneal and follicular fluid from infertile women with endometriosis and fertile women without the disease. The extent of the disease was staged according to the revised American Fertility Society classification (1997). Serum and peritoneal fluid were collected from 49 women aged 19 to 39 years undergoing laparoscopy. Eighteen women had stage I-II endometriosis and 10 had stage III-IV. Controls were 21 women undergoing laparoscopy for tubal sterilization. Follicular fluid was obtained from 39 women aged 25-39 years undergoing in vitro fertilization (21 infertile women with endometriosis and 18 infertile women without endometriosis). Serum prolactin levels were significantly higher in infertile women with stage III-IV endometriosis (28.9 +/- 2.1 ng/mL) than in healthy controls (13.2 +/- 2.1 ng/mL). Serum cortisol levels were significantly higher in infertile women with stage III-IV endometriosis (20.1 +/- 1.3 ng/mL) than in controls (10.5 +/- 1.4 ng/mL). Cortisol and prolactin levels in follicular fluid and peritoneal fluid did not differ significantly between groups. The high levels of cortisol and prolactin in the serum from women with endometriosis might contribute to the subfertility frequently associated with the disease. Moreover, since higher levels of cortisol and prolactin are often associated with stress, it is probable that stress might contribute to the development of endometriosis and its progression to advanced stages of the disease.

Prolactin and cortisol levels in women with endometriosis

Endometriosis is a progressive estrogen-dependent disease affecting women during their reproductive years. The objective of the present study was to investigate whether endometriosis is associated with stress parameters. We determined cortisol and prolactin levels in serum, peritoneal and follicular fluid from infertile women with endometriosis and fertile women without the disease. The extent of the disease was staged according to the revised American Fertility Society classification (1997). Serum and peritoneal fluid were collected from 49 women aged 19 to 39 years undergoing laparoscopy. Eighteen women had stage I-II endometriosis and 10 had stage III-IV. Controls were 21 women undergoing laparoscopy for tubal sterilization. Follicular fluid was obtained from 39 women aged 25-39 years undergoing in vitro fertilization (21 infertile women with endometriosis and 18 infertile women without endometriosis). Serum prolactin levels were significantly higher in infertile women with stage III-IV endometriosis (28.9 ± 2.1 ng/mL) than in healthy controls (13.2 ± 2.1 ng/mL). Serum cortisol levels were significantly higher in infertile women with stage III-IV endometriosis (20.1 ± 1.3 ng/mL) than in controls (10.5 ± 1.4 ng/mL). Cortisol and prolactin levels in follicular fluid and peritoneal fluid did not differ significantly between groups. The high levels of cortisol and prolactin in the serum from women with endometriosis might contribute to the subfertility frequently associated with the disease. Moreover, since higher levels of cortisol and prolactin are often associated with stress, it is probable that stress might contribute to the development of endometriosis and its progression to advanced stages of the disease.

Testosterona e gonadotrofina coriônica humana estimulam a esteroidogênese em células da granulosa de folículo pré-ovulatório de égua? / Do testosterone and human chorionic gonadotropin stimulate steroidogenesis in granulosa cells of preovulatory follicle in mare?

Avaliou-se o papel da gonadotrofina coriônica humana (hCG) e da testosterona na produção de progesterona (P4) e 17ß-estradiol (E2) pelas células da granulosa cultivadas in vitro de folículo antral de égua. Os tratamentos usados foram: 1- controle (nenhum hormônio adicionado), 2- 1UI hCG (0,3µg/ml) e 3- 10UI hCG (3,0µg/ml). O tratamento com hCG foi realizado na presença ou não de testosterona (144ng/ml). O meio foi coletado e substituído com 0,25, 3, 6, 12, 24 e 144h de cultivo. As concentrações de P4 e E2 foram mensuradas por radioimunoensaio. Não se observou diferença entre os tratamentos 1 e 3 quanto à produção de P4 e E2; o tratamento 1 resultou em aumento da concentração de progesterona após 24h de cultura (P<0,01), mas somente em presença de testosterona. A concentração de estradiol aumentou em presença de testosterona, alcançando concentração máxima com 6h de cultura (P<0,01), e diminuiu gradativamente, até atingir a concentração observada com 0,25h de cultura. A adição de hCG não influenciou a síntese do estradiol. A testosterona desempenhou importante efeito estimulador na síntese/secreção doe E2 pelas células da granulosa e modulou a ação do hormônio luteinizante na diferenciação e luteinização das células da granulosa de folículo antral presumidamente pré-ovulatório de égua in vitro.

Testosterona e gonadotrofina coriônica humana estimulam a esteroidogênese em células da granulosa de folículo pré-ovulatório de égua? / Do testosterone and human chorionic gonadotropin stimulate steroidogenesis in granulosa cells of preovulatory follicle in mare?

Avaliou-se o papel da gonadotrofina coriônica humana (hCG) e da testosterona na produção de progesterona (P4) e 17ß-estradiol (E2) pelas células da granulosa cultivadas in vitro de folículo antral de égua. Os tratamentos usados foram: 1- controle (nenhum hormônio adicionado), 2- 1UI hCG (0,3µg/ml) e 3- 10UI hCG (3,0µg/ml). O tratamento com hCG foi realizado na presença ou não de testosterona (144ng/ml). O meio foi coletado e substituído com 0,25, 3, 6, 12, 24 e 144h de cultivo. As concentrações de P4 e E2 foram mensuradas por radioimunoensaio. Não se observou diferença entre os tratamentos 1 e 3 quanto à produção de P4 e E2; o tratamento 1 resultou em aumento da concentração de progesterona após 24h de cultura (P<0,01), mas somente em presença de testosterona. A concentração de estradiol aumentou em presença de testosterona, alcançando concentração máxima com 6h de cultura (P<0,01), e diminuiu gradativamente, até atingir a concentração observada com 0,25h de cultura. A adição de hCG não influenciou a síntese do estradiol. A testosterona desempenhou importante efeito estimulador na síntese/secreção doe E2 pelas células da granulosa e modulou a ação do hormônio luteinizante na diferenciação e luteinização das células da granulosa de folículo antral presumidamente pré-ovulatório de égua in vitro.(AU)

The role of the human chorionic gonadotropin (hCG) and testosterone was evaluated in the progesterone (P4) and estradiol-17b (E2) production by granulosa cells of antral follicles from mare cultivated in vitro. The treatment (groups) with gonadotropin consisted of: 1- control (no added hormone); 2- 1 IU hCG (0.3mg/ml) and 3- 10 IU hCG (3.0mg/ml). The treatment with hCG was carried out in the presence or not of testosterone (144ng/ml). The culture medium was collected and replaced at 0.25, 3, 6, 12, 24 and 144h of culture. The concentrations of P4 and E2 were measured by radioimunoassay. Analyses of variance were used for P4 and E2, and mean of the factors were compared by the Tukey test at 5% of probability. No difference was observed between 1 and 2 groups. Treatment with 1 IU of hCG increased progesterone concentration after 24h of culture (P<0.01), only in the presence of testosterone. The concentration of estradiol increased in the presence of testosterone, reaching maximum concentration with 6h of culture (P<0.01), and reduced gradually until the observed concentration at 0.25h of culture. The addition of hCG had no effect in the synthesis of this steroid. The testosterone modulates the action of the luteinizing hormone in the differentiation and luteinization of the granulosa cells and plays important estimulator effect in the synthesis/secretion of E2 by granulosa cells in vitro of presumptive pre-ovulatory antral follicle in mare.(AU)

Vascular non-endothelial nitric oxide induced by swimming exercise stress in rats.

1. Herein, we report the effects of acute or chronic forced swimming on vascular responsiveness to angiotensin (Ang) II. 2. The possible involvement of locally produced substances, such as nitric oxide (NO) and prostanoids, in these effects were studied in rat thoracic aorta and superior mesenteric arteries. 3. Chronic, but not acute, swimming reduced the efficacy (maximal effect; Emax) of AngII in thoracic aorta and mesenteric arteries, either with intact or denuded endothelium. 4. The efficacy of AngII was reduced in the presence of indomethacin in mesenteric arteries, but not in the aorta, from either control or chronically stressed rats. 5. Treatment with NG-monomethyl-l-arginine reversed the effect of chronic stress on the response to AngII, suggesting that chronic stress may increase non-endothelial NO activity in both the aorta and mesenteric arteries. 6. The effects of acute and chronic stress on vascular reactivity were selective for AngII because no changes were observed on the effects of phenylephrine.

LH response (in vivo and in vitro) to an LHRH agonist administered to domestic male cats.

We investigated plasma luteinizing hormone (LH) concentration in domestic male cats challenged with Luteinizing Hormone Releasing Hormone Analog (LHRH-A) [des Gly 10, (DTrp6)-LHRH ethylamide] that mediates the function of the hypothalamic-pituitary-gonadal axis (HPG). Plasma LH concentrations in cats treated daily with LHRH (10 microg/100 microl/kg/day, subcutaneously-s.c.) for 19 days (LHRH group) and in controls treated with saline (NaCl-0.9%, same volume-SAL group) were chronically studied. LHRH administration (s.c.) for 15 days induced a significant fall (P < 0.05) in plasma LH concentrations during the chronic study. After the 15th day of treatment the groups were divided once more into animals treated with LHRH (10 microg/100 microl/kg) or saline (i.v.), and a time course study (300 min) was performed (acute study). Next, four groups of cats were compared in an acute study involving the s.c./i.v. administration of SAL/SAL, SAL/LHRH, LHRH/SAL, and LHRH/LHRH. The responses of the SAL animals challenged by acute i.v. administration of LHRH (group SAL/LHRH) were significantly higher (P < 0.01) than those of animals treated with LHRH (sc) (group LHRH/LHRH). LH release was also significantly increased in the latter group (P < 0.05), although the effect was short lasting, being recorded only at the first observation (45 min). An in vitro study with the pituitaries was also performed on day 20. Mean (+/-SEM) LH concentrations in the culture medium containing pituitaries with LHRH (10(-7) M) or saline were determined. In vitro analysis of these pituitaries demonstrated a significantly reduced response (P < 0.05) by animals treated sc with LHRH for 19 days. This study represents a source of data for the domestic cat going beyond its own physiology. Serving as a model, this animal provide important information for the study of reproductive physiology in other members of its family (Felidae), almost all of them threatened with extinction.

Changes in sympathetic nerve activity of the mammalian ovary during a normal estrous cycle and in polycystic ovary syndrome: Studies on norepinephrine release.

Although it has been known for many years that the ovary is innervated by catecholaminergic nerve fibers and much experimental evidence has strengthened the notion that catecholamines are physiologically involved in the control of ovarian function, scarce evidence has been presented as to the role of sympathetic activity in ovarian pathologies that affect reproductive function. The purpose of this article is to provide a succinct overview of the findings in this area and discuss them relative to the pathology of polycystic ovary syndrome, the most common ovarian pathology in women during their reproductive years.

Steroidogenesis in cumulus cells of bovine cumulus-oocyte-complexes matured in vitro with BSA and different concentrations of steroids.

The present in vitro experiments were designed to evaluate the ability of bovine cumulus-oocyte-complexes (COCs) to produce steroids and also to evaluate the modulatory effects of added estradiol, progesterone and testosterone on the steroidogenic activity of COCs. Considerable estradiol accumulation was observed in the control maturation medium for in vitro maturation of bovine COCs during the 24h of maturation (P<0.05). When testosterone was added to the medium at various concentrations, a slight estradiol accumulation occurred, which, however, was lower (P<0.05) than that observed in the control medium. Slight estradiol accumulation was observed in maturation medium containing progesterone at concentrations of 2.5, 5.0 and 10.0 microg/ml, but these increases were less (P<0.05) than those observed in the control medium. However, in the presence of 1.0 microg/ml progesterone, estradiol accumulation was equal to that of the control medium (P>0.05). Progesterone accumulation (P<0.05) was observed in the control medium for in vitro maturation of bovine COCs. When estradiol was added to the maturation medium, progesterone accumulation was observed, but was significant (P<0.05) only when the medium was supplemented with the lesser concentrations of estradiol utilized in the experiment (1.0 microg/ml). The results demonstrated that (1) cumulus cells of bovine COCs are able to secrete estradiol and progesterone in culture systems for in vitro maturation, and this steroidogenesis is modulated by the steroids progesterone, testosterone and estradiol, and (2) the addition of estradiol to the in vitro maturation medium of bovine oocytes should be reviewed, since cumulus cells of COCs have been demonstrated to secrete estradiol in the maturation medium.

Influência da alimentaçäo no teste de absorçäo e tolerância à glicose em eqüinos submetidos a diferentes períodos de jejum / Influence of nutrition on the glucose absorption and tolerance test in horses submitted to different fasting periods

Quatro grupos de eqüinos da raça Brasileiro de Hipismo foram submetidos a jejuns de 24 e 48 horas com a finalidade de se estudar a capacidade de absorçäo do intestino delgado. Dois grupos foram alimentados unicamente com capim coast cross (Cynodon dactylon). Os outros dois grupos, além de pasto de coast cross, receberam suplementaçäo com gräos. Ao final dos períodos de jejum, os animais receberam 1g de glucose/kg de peso corporal, em soluçäo a 20 por cento, por sonda nasogástrica. Amostras de sangue foram colhidas imediatamente antes, 30, 60, 120, 180, 240, 300 e 360 minutos após a administraçäo de glicose, para determinaçäo da glicemia pelo método da ortotoluidina e da insulina, pelo uso do radioimunoensaio. Os animais que receberam alimento concentrado apresentaram maiores aumentos na glicemia e na insulinemia que aqueles mantidos apenas em regime de pasto. O período de jejum de 48 horas induziu concentraçöes mais elevadas de glicemia e de insulinemia que o jejum de 24 horas

Decreased spermatogenic and androgenic testicular functions in adult rats submitted to immobilization-induced stress from prepuberty

We investigated whether chronic stress applied from prepuberty to full sexual maturity interferes with spermatogenic and androgenic testicular functions. Male Wistar rats (40 days old) were immobilized 6 h a day for 60 days. Following immobilization, plasma concentrations of corticosterone and prolactin increased 135 per cent and 48 per cent, respectively, while plasma luteinizing hormone and testosterone presented a significant decrease of 29 per cent and 37 per cent, respectively. Plasma concentration of follicle-stimulating hormone was not altered in stressed rats. Chronic stress reduced the amount of mature spermatids in the testis by 16 per cent and the spermatozoon concentration in the cauda epididymidis by 32 per cent. A 17 per cent reduction in weight and a 42 per cent decrease in DNA content were observed in the seminal vesicle of immobilized rats but not in its fructose content. The growth and secretory activity of the ventral prostate were not altered by chronic stress.

Chemical sympathectomy blocks androgen biosynthesis during prepuberty

Twenty-one-day old male Wistar rats were injected subcutaneously with guanethidine (GUA) at doses of 5 and 10 mg kg-1 day-1 for 20 days. Animals were sacrificed by decapitation during the prepubertal (41 days of age) and early-pubertal (51 days of age) periods of sexual development. The tests were collected, frozen in liquid N2 and stored at -70oC until determination of testicular progesterone (P), androstenedione (A) and testosterone (T). Higher levels of P (2.18 +/- 0.24 ng/g, control = 1.24 +/- 0.16 ng/g) associated with decreased with decreased levels of androgens (A = 0.26 +/- 0.06 ng/g T = 2.05 +/- 0.19 ng/g; control = 1.86 +/- 0.76 ng/g and 8.48 +/- 1.16 ng/g, respectively) were observed in 10 mg GUA-treated rats of prebubertal age, while only P levels (3.12 +/- 0.51 ng/g, control = 1.73 +/- 0.27 ng/g) were incresead in rats of early pubertal...

Relationship between plasma 17-beta estradiol on the day of estrus and number of viable embryos in Bos indicus (Nellore) cows superovulated with FSH

Thirteen cows, Bos indicus, of the Nellore breed were superovulated with 22 mg of follicle stimulating hormone (FSH) administered by intramuscular route during four consecutive days (D10, D11, D12 and D13), starting on the 10th day of the estrous cycle (day 0 = estrus). Prostaglandin (PGF2 alpha, 1.0 mg, im) was administered on D12, 48 h after the first FSH injection, for the induction of estrus on D14, when artificial insemination was performed. Seven days later (D21 of the cycle), embryos were collected, and evaluated, and the ovarian response was estimated on the basis of number of corpora lutea determined by rectal palpation. Blood samples were obtained for the determination of plasma 17-beta estradiol on D10, D11, D12, D13, D14 and D21 and plasma progesterone on D14 by RIA. The donors were divided into two groups according to progesterone levels on D14, the day of the induced estrus (GI: P4 < or = 1.00 ng/ml, N = 5 and GII: P4 > 1.00 ng/ml, N = 8). A linear positive correlation was observed between plasma 17-beta estradiol concentration on the day of estrus and viable embryo number. We conclude that plasma 17-beta estradiol and progesterone concentrations on the day of estrus can be used to predict the viability of embryos recovered from Nellore cows superovulated with FSH.

Acute administration of human chorionic gonadotropin reverts some of the inhibitory effects of an LH-RH agonist on testicular steroidogenesis

An LH-RH agonist, des-Gly10, [DTrp6]-LH-RH ethylamide (LH-RH A), was administered chronically to adult male cats in order to determine its effect on the steroidogenesis of the testis during the stimulatory action of human chorionic gonadotropin (hCG). Measurement of plasma testosterone levels were combined with the histochemical analysis of some steps of the testicular steroidogenic pathway. Chronic daily treatment with LH-RH A(20 *g/kg) for 67 days inhibited the early testicular response to hCG during the initial 0.5,1 and 24 h, whereas the inhibitory egffect was not observed 48 and 72 h after hCG administration.The maximal responses to hCG were obtained both in LH-RH A-treated animals and in their control group 48 and 72 h after hCG adnministration. Under these conditions, LH-RH A-treated cats showed no alteration in 3ß-hydroxysteroid dehydrogenase (3ß-Host-D) activity, whereas a marked inhibition was observed in the activity of alcohol dehydrogenase (ADII) which reflects the activity of 20,22-desmolase and/or 17,20-desmolase.