Practical considerations for TLD-400/700-based gamma ray dosimetry for BNCT applications in a high thermal neutron fluence.

Operating experience with thermoluminescent dosimeters used in a boron neutron capture therapy research project is reported. In particular, certain facets of the use of thermoluminescent dosimeters for gamma ray dose measurements in the presence of a high thermal neutron fluence are discussed, including a comparison of TLD-400 and TLD-700 for gamma ray dosimetry, annealing procedures, and the effects of neutrons (56Mn activation) on TLD-400. The TLD-400 were observed to have a thermal neutron sensitivity (due to 56Mn beta decay) of 1.5 x 10(-13) Gy per n cm-2. An algorithm was developed to correct for the 56Mn beta decay thermal neutron-induced effects on TLD-400 by using a two-stage thermoluminescent readout for the thermoluminescent dosimeter chips.

Effect of the antiglucocorticoid RU486 on adrenal steroidogenic enzyme activity and steroidogenesis.

RU486, a synthetic steroid receptor antagonist, has strong antiprogesterone and antiglucocorticoid properties. Chronic RU486 administration in two patients with ectopic secretion of adrenocorticotropin (ACTH) has been associated with decreasing plasma cortisol concentrations. One explanation of this finding is that RU486 may directly inhibit adrenal steroidogenesis. To test this hypothesis, we measured the effect of RU486 on specific steroidogenic enzymatic steps using an in vivo rat and an in vitro monkey model. Hypophysectomized-castrated-ACTH-replaced Sprague-Dawley rats were given RU486 i.p. at daily doses of 0, 0.0005, 0.005, 0.05, 0.5 and 5 mg/kg body weight per day for 7 days. The animals were sacrificed, and blood and adrenal glands collected. Adrenal cortical mitochondria and microsomes were purified from the rats and from two untreated Cynomolgus macaque monkeys. Specific steroidogenic enzyme activities were measured in the rat by the incorporation of 14C-labeled steroid substrates into products. A similar protocol was used to assay the steroidogenesis in the monkey adrenal fractions in the presence and absence of added RU486. Although rat adrenal weights decreased significantly at the highest RU486 dose, plasma levels of corticosterone were similar in control and treated rats. Rat adrenal 3 beta-hydroxysteroid dehydrogenase/isomerase (3-HSD), 21-hydroxylase (21-OH) and 11-hydroxylase (11-OH) activities decreased with increasing RU486 doses, with 21-OH and 11-OH being most severely affected. Monkey adrenal 3-HSD, 21-OH, 11-OH, 17-hydroxylase and 17,20-desmolase similarly decreased in the presence of increasing in vitro concentrations of RU486.(ABSTRACT TRUNCATED AT 250 WORDS)

Oestrogen modulation with parturition in the human placenta.

An initial group of term (36-41 6/7 weeks), preterm (less than 36 weeks), and post-term (42 or more weeks) placentae were collected from women at delivery to determine the placental levels of important steroids and steroidogenic enzymes involved in the oestrogen synthesis pathway as a function of gestational age. A second group of placentae were obtained from women delivering at term before and after the onset of labour. Placentae were evaluated individually for cytosolic steroid hormone levels and microsomal steroidogenic enzyme activities. Oestradiol (E2), oestrone (E1), progesterone (P), and delta-4-androstenedione (A) were measured by radioimmunoassay in placental cytosols. Aromatase (AR), sulphatase (S), and 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta HSD) activities were assayed in placental microsomes. Cytosolic concentrations of E1, E2, P, and A did not differ with respect to gestational age. Correspondingly, the microsomal enzyme activities of 3 beta HSD, S, and AR did not vary as a function of gestational age. However, when patients at term who were in labour prior to delivery were compared to those who were not, the placental cytosolic level of E1 was found to be threefold higher in the non-labouring group (4572 versus 1427 pg/mg cytosolic protein, P < 0.025). Additionally, microsomal aromatase activity was also significantly higher in the non-labouring patients (46 versus 19 pM/min/mg protein, P < 0.025), while the E2 to P ratio in the labouring patients was twice that of the non-labouring group, a difference which was significant at the P < 0.025 level (Wilcoxon rank sum test). These data suggest that at term, prior to labour, the placental production of E1 by AR is high, and that AR activity and E1 levels fall significantly after the onset of labour. Also, the placental cytosolic concentration of the more active oestrogen, E2, demonstrates stable to rising levels with a significant increase in E2/P after the onset of labour. We theorize that in the term pregnancy prior to labour, E1 may represent a large but relatively inactive intracellular oestrogen pool which is maintained by high AR activity, and may function to protect the pregnant local uterine environment from the more oxytocic effects of E2.

Enhanced follicle regulatory protein levels accompany reinitiation of ovulatory function after parturition.

OBJECTIVES: We examined the changes in follicle regulatory protein, estrone-3-glucuronide, pregnanediol-3-glucuronide, and luteinizing hormone levels in first-morning urine samples from postpartum, fully breast-feeding women to characterize the reemergence of these urinary hormones after pregnancy ovarian quiescence and early postpartum period and to determine whether follicle regulatory protein could be used prospectively to predict the return of fertility. STUDY DESIGN: Twenty-five hundred urine samples collected from six postpartum women were evaluated. Daily urine samples collected from normally cycling women were used to establish normal urinary hormone and hormone metabolite cyclicity. Luteinizing hormone, estrone-3-glucuronide, and pregnanediol-3-glucuronide levels were measured by radioimmunoassay. Follicle regulatory protein level was assayed with a double-antibody enzyme-linked immunosorbent assay. RESULTS: Although follicle regulatory protein levels were found to be very low or undetectable in early postpartum urine, they began to rise with episodes of estrone-3-glucuronide and pregnanediol-3-glucuronide secretion. A chi 2 analysis suggests that increasing urinary follicle regulatory protein levels are most closely associated with the luteal phase of the first menstrual cycles in postpartum women. CONCLUSIONS: These results suggest that follicle regulatory protein is of little value in predicting either the onset of renewed ovarian activity or the fertile period.

Effects of vehicle supplementation on total estradiol absorption from a transdermal estradiol delivery system.

OBJECTIVE: To evaluate the effects of vehicle supplementation on serum estradiol (E2) delivery pharmacokinetics from the Ciba-Geigy (Summit, NJ) 0.1-mg Estraderm Patch. DESIGN: Postmenopausal women were randomized to a 28-day crossover treatment protocol separated by a 14-day wash out period. SETTING: Normal human volunteers were studied in an academic research environment. PATIENTS, PARTICIPANTS: The subject pool included eight healthy postmenopausal women between 32 and 60 years of age. INTERVENTIONS: In treatment A, a 0.1-mg Estraderm Patch was worn for 7 days; in treatment B, and identical patch was worn into which 0.6 mL of ethanol was injected on day 3 of use. MAIN OUTCOME MEASURES: Serum E2 levels were measured in both groups. RESULTS: Although E2 absorption showed characteristic interpatient variability, addition of ethanol significantly extended the mean time for serum E2 levels to return to baseline, without increasing peak absorption. The mean extension was 50 hours. CONCLUSION: The addition of ethanol to the Estraderm Patch increased the duration of elevated serum E2 levels measured in menopausal women, thus potentially increasing the effective life span of the transdermal therapeutic system.

Genetic variation of the glucocorticoid receptor from a steroid-resistant primate.

The neotropical cotton-top marmoset (Saguinus oedipus) is a New World primate known to have markedly increased total and free plasma cortisol concentrations when compared with Old World primates including man. The relative end-organ 'resistance' to glucocorticoids found in various New World primates has been attributed to a glucocorticoid receptor (GR) with diminished affinity for glucocorticoids. It has been demonstrated that the marmoset GR has approximately tenfold lower binding affinity for dexamethasone when compared with the human GR. We have examined the primary structure of the marmoset GR by molecular cloning and sequencing of GR functional domains. A library of cDNA clones was constructed in the phage vector gamma gt10 using poly(A)+ RNA from a marmoset-derived lymphoid cell line, and screened using the human GR cDNA. DNA sequencing determined 76 individual nucleotide substitutions in the coding region of the marmoset GR. Comparison of the marmoset GR nucleotide sequence with the human GR cDNA coding region indicated an overall sequence homology of about 97%. Thirty of the nucleotide substitutions lead to alterations in the predicted amino acid sequence (28 amino acid substitutions) of the marmoset GR. The size of the marmoset GR predicted from the 778 amino acids is approximately 90,000 which is in agreement with previous size estimates of the human and marmoset GRs. Alterations of amino acid sequence in the marmoset GR were greatest towards the amino terminus, including the tau 1 domain putatively involved in transcriptional activation. The DNA-binding domain contained an additional codon (arginine).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of gossypol on adrenal function.

Gossypol, an antifertility agent, has inhibitory actions on many membrane-associated enzymes, suggesting that this agent might have a generalized effect on cell membranes. This hypothesis was examined in the present study using membranes and dispersed cells prepared from human and rat adrenal glands. Four parameters were determined: microviscosity as measured by fluorescence polarization of human adrenal microsomal- and mitochondrial-enriched membranes, adrenal steroidogenic enzymes; and cAMP and cortisol responses to ACTH. It was found that gossypol increased the polarization constants of microsomes and mitochondria in a dose-dependent manner. Of the three adrenal enzymes tested, both 3 beta-hydroxysteroid dehydrogenase delta 5-delta 4 isomerase and 11-hydroxylase were inhibited by gossypol, but not 21-hydroxylase. Using intact human adrenocortical cells, high doses of gossypol also inhibited the ACTH-stimulated cAMP and cortisol levels. The in vivo corticosterone response to ACTH in rats subjected to chronic gossypol treatment was also found to be reduced. These findings suggest that gossypol has multiple effects on adrenal function. Its effects on membrane microviscosity, adrenal steroidogenesis, cAMP and corticosterone responses to ACTH stimulation probably occur through a generalized membrane effect.

A novel testis-stimulating factor in familial male precocious puberty.

BACKGROUND: Familial male precocious puberty is a gonadotropin-independent form of precocious puberty that occurs only in males. The cause of the disorder is unknown. To examine the hypothesis that the plasma of boys with familial male precocious puberty contains a novel stimulator of testicular testosterone production, we developed a bioassay using adult male cynomolgus monkeys. METHODS: We collected plasma from 12 boys with familial male precocious puberty, 7 normal prepubertal boys of similar ages and with similar plasma gonadotropin levels, and 1 boy with hypogonadotropic hypogonadism and infused it into the testicular artery of adult male cynomolgus monkeys that had been pretreated with gonadotropin-releasing-hormone antagonist to inhibit the endogenous secretion of gonadotropins. Testicular venous effluent was collected at 15-minute intervals for 3 or 5 hours for the measurement of testosterone. RESULTS: The mean (+/- SE) peak testosterone response, as compared with base line, was significantly greater in the monkeys infused with plasma from the 12 boys with familial male precocious puberty than in the monkeys infused with plasma from the 7 normal prepubertal boys and the boy with hypogonadotropic hypogonadism (385 +/- 51 vs. 184 +/- 25 percent, P less than 0.005) in the three-hour studies. Plasma from 92 percent of the boys with familial male precocious puberty and 12.5 percent of the normal prepubertal boys stimulated a response greater than 195 percent of base-line values. In the animals studied for five hours after receiving a second dose of antagonist, the mean peak testosterone response, as compared with base line, was significantly greater in the monkeys infused with plasma from three boys with familial male precocious puberty than in the monkeys infused with plasma from three normal prepubertal boys (363 +/- 81 vs. 115 +/- 6 percent, P less than 0.01). The mean area under the testosterone-response curve was significantly larger in the monkeys infused with plasma from the boys with familial male precocious puberty in the five-hour studies (154 +/- 34 vs. -58 +/- 10 percent, P less than 0.005), but not in the three-hour studies. CONCLUSIONS: These findings support the presence of a circulating testis-stimulating factor in the plasma of boys with familial male precocious puberty. The production of such a factor would explain the biologic nature of the disorder.

Calcium metabolism in postpartum lactation: the effect of estrogen status.

Postpartum lactation represents a unique state of increased calcium demand in which women are also hyperprolactinemic and hypoestrogenic. This is associated with increased calcium mobilization from bone and bone loss. To better understand the effect of estrogen (E) status on calcium metabolism during lactation, we studied 10 long-term lactating women at 12 weeks postpartum when they were hypoestrogenic and again at 37.4 +/- 3.4 (+/- SD) weeks during the midfollicular phase of their second ovulatory cycle. Urinary and serum markers of calcium metabolism were measured at these intervals. The results revealed that when E was low, osteocalcin and hydroxyproline were increased with a lower circulating parathyroid hormone (PTH) level, whereas reciprocal changes were noted when E was increased. The findings suggest that E status can modulate PTH's ability to mobilize one's stores of calcium.

Steroidogenic enzyme activities, morphology, and receptor studies of a testicular adrenal rest in a patient with congenital adrenal hyperplasia.

Steroid-secreting tumors of the testis have generally been considered to be of Leydig cell origin. Testicular tumors in patients with congenital adrenal hyperplasia have been thought to be adrenal rests, but no conclusive evidence supporting the hypothesis has been presented. We report a morphological and biochemical analysis of a patient with 21-hydroxylase deficiency who developed bilateral nodular hyperplasia of steroid-secreting tissue within the testis, despite suppression therapy with both exogenous glucocorticoids and testosterone. The tissue was formed of confluent nodules of homogenous cells. Electron microscopy showed the cells to have abundant smooth endoplasmic reticulum, well developed Golgi apparatus, and mitochondria with predominantly tubular cristae, features characteristic of steroid-secreting cells of adrenocortical origin. Crystals of Reinke were not observed. Functional studies in vivo showed a marked response to ACTH infusion, with 17-hydroxyprogesterone rising from 56 to 13,500 ng/mL, cortisol from less than 2 to 19 micrograms/dL, and testosterone from 369 to 629 ng/dL, with an attendant increase in testicular size and pain over 48 h. Receptor studies in vitro revealed no gonadotropin receptors, but abundant angiotensin-II receptors. Enzyme activity analysis in vitro showed undetectable 21-hydroxylase activity and an enzyme profile consistent with adrenocortical cells rather than Leydig cells. Based on these morphological and biochemical findings, we conclude that the nodular steroidogenic tissue that replaced this patient's testes was of adrenal origin. The study documents for the first time the development of adrenocortical tumors from adrenal rest tissue within the testis.

The inhibition of human adrenal steroidogenic enzyme activities by suramin.

Suramin has recently been used to treat patients with acquired immune deficiency syndrome because of the action of this drug on reverse transcriptase. Patients so treated developed the symptoms and hormonal profiles of adrenal insufficiency. To evaluate the mechanism of action of suramin on adrenalcortical function, adrenal mitochondrial and microsomal preparations from five subjects were assayed for steroidogenic enzyme activity in the presence and absence of suramin. Specifically, 3 beta-hydroxysteroid dehydrogenase/isomerase, 17 alpha-hydroxylase, 21-hydroxylase, 11 beta-hydroxylase, and 17,20-desmolase activities were measured in the presence of 0-5000 mumol/L suramin concentrations. In all assays, enzyme activities decreased in a dose-dependent fashion as suramin concentrations increased. The drug doses (calculated) that caused 50% inhibition of enzyme activity were: 21-hydroxylase activity, 50 mumol/L; 17 alpha-hydroxylase activity, 25 mumol/L; 17,20-desmolase activity, 50 mumol/L; 11 beta-hydroxylase, 2 mumol/L, and 3 beta-hydroxysteroid dehydrogenase/isomerase, 1200 mumol/L. These results suggest that suramin has a concentration-dependent inhibitory effect on the key P-450-regulated enzymatic steps in adrenal glucocorticoid steroidogenesis, which may explain the development of adrenal insufficiency in acquired immune deficiency syndrome patients treated with suramin.

The effect of ketoconazole on steroidogenesis: I. Leydig cell enzyme activity in vitro.

The in vitro inhibition of Leydig cell microsomal steroidogenesis by ketoconazole, a potent P-450 dependent enzyme blocker, was evaluated in the human, stallion and pig. Purified Leydig cells were isolated by mechanical dispersion of teased, decapsulated whole testes and sieving through a 0.25 mm stainless steel mesh. The activity of 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD), 17-hydroxylase (17-OHase), 17,20-desmolase (17,20D), 17-ketosteroid reductase (17-KSR) and aromatase were measured using a constant amount (50 microM) of 14C-labelled substrates in the presence of varying concentrations of pure ketoconazole. Products were isolated by thin layer chromatography and verified by derivative formation. 17-OHase and 17,20D activities were significantly inhibited (p less than .001) by ketoconazole at concentrations as low as 5 microM. 3 beta-HSD, 17-KSR and aromatase activities were only significantly inhibited by ketoconazole at concentrations of 500 and 5000 microM. These data describe the specific loci of inhibition of ketoconazole on testicular steroidogenesis and confirm the observations that ketoconazole is an effective inhibitor of androgen biosynthesis in several species.

The effect of ketoconazole on steroidogenesis. II. Adrenocortical enzyme activity in vitro.

The activity of five adrenocortical steroidogenic enzymes, 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD), 17-hydroxylase (17-OHase) 17,20 desmolase (17,20D), 21-hydroxylase (21-OHase) and 11-hydroxylase (11-OHase), were measured in vitro in purified mitochondria or microsomes from rhesus monkey (Macaca mulata) and human adrenal tissue in the presence and absence of graded concentrations of ketoconazole. Rhesus 3 beta-HSD activity was unaffected by ketoconazole at concentrations up to 5000 microM. However, human adrenal 3 beta-HSD was inhibited by approximately 40% (p less than .01) at concentrations of 500 microM and by 80% at 100 microM. 17-OHase and 17,20D were significantly inhibited in the human at 5 microM (p less than .001) and in the rhesus monkey at 50 microM (p less than .001). A similar inhibitory effect was found on microsomal 21-OHase, with significant inhibition at 5 microM ketoconazole in the human and rhesus monkey (p less than 0.001). Mitochondrial 11-OHase was also significantly inhibited by ketoconazole in both the human (p less than .005) and rhesus (p less than .001) at 2.0 microM. These results represent documentation of the specific adrenal steroidogenic steps affected by ketoconazole and confirm the observations that this imidazole derivative is a powerful inhibitor of enzymes in the glucocorticoid pathway.

Ketoconazole inhibits multiple steroidogenic enzymes involved in androgen biosynthesis in the human ovary.

Ketoconazole (KZ) has been shown to inhibit testicular and adrenal steroidogenesis and is useful in the medical management of gonadotropin-independent precocious puberty, prostatic cancer, and Cushing's syndrome. To determine whether KZ similarly affects ovarian steroidogenesis, the authors examined its effect on the activity of the human ovarian 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD), 17-hydroxylase (17-OH), and aromatase (AR) in vitro. A dose-dependent decrease in the activities of 3 beta-HSD and 17-OH was observed with increasing amounts of KZ. With 10, 50, and 100-fold excess KZ, the activity of 3 beta-HSD decreased by 59% (P less than 0.001), 73% (P less than 0.005), and 85% (P less than 0.005), respectively. At equimolar concentrations with substrate (50 microM), KZ inhibited 17-OH by 70% (P less than 0.01). No significant effect on ovarian AR activity was observed, except at the highest concentration of KZ tested. The authors conclude that low concentrations of KZ profoundly inhibit the activity of human ovarian 3 beta-HSD and 17-OH in vitro. These observations suggest that KZ might be useful in the medical management of women with hyperandrogenism, but further experimentation and clinical trials will be necessary.

The prediction of ovulation and monitoring of the fertile period.

Simple and reliable methods have been sought for both predicting and confirming ovulation. Application of these methods could include management of infertile couples to aid in conception and for increasing the reliability of natural family planning (NFP) as a method of birth control. With the advent of specific hormone assays, serial measurements of estrogens, progesterone (and metabolites), and luteinizing hormone have been the gold standard of monitoring ovarian function in women. However, newer and simpler methodologies have been described and are currently either in use or being tested. These include the measurement of basal body temperature (BBT), the evaluation of the volume, consistency and electro-conductivity of cervicovaginal fluid, salivary steroid content and cellular enzymatic activity, the use of enzyme-linked immunosorbent assays applied to solid-phase formats, and the investigation of new hormonal molecules as markers of reproductive state and function. These new technologies are described herein and their potential for monitoring ovarian function is discussed.

Effect of the antiprogestin RU486 on human ovarian steroidogenesis.

Previous studies in the authors' laboratory suggest that the antiprogestin RU486 may directly affect human ovarian progesterone production. The possibility that this compound could affect other steps in human ovarian steroidogenesis was examined by studying its effects on estrogen production in cultured human granulosa cells and on human ovarian aromatase (AR) and 17-hydroxylase (17-OH) activities in vitro. RU486 had no effect on media estradiol (E2) levels as measured by radioimmunoassay (RIA) over a 24-hour incubation period. Furthermore, no effect on ovarian AR activity occurred at concentrations of RU486 100 times substrate. However, a dose-dependent decrease in the activity of 17-OH was observed with increasing amounts of drug. RU486 decreased 17-OH activity by 12 and 29% below that of basal activity at concentrations equal to and ten times substrate. At 50- and 100-fold excess, RU486 further decreased 17-OH activity by 42 (P less than 0.01) and 48% (P less than 0.005). In conclusion, RU486 directly inhibits human ovarian 17-OH activity, but does not affect AR activity or E2 production in vitro. Clinically observed decreases in serum E2 levels may be due to inhibition of enzymatic steps proximal to E2 synthesis. These findings support the authors' previous observations suggesting that RU486 has a direct affect on human ovarian steroidogenesis.

Adrenal 11-hydroxylase activity in a hypercortisolemic New World primate: adaptive intra-adrenal changes.

The squirrel monkey, a representative New World primate, has high plasma cortisol and aldosterone concentrations when compared to Old World primates. We measured adrenal mitochondrial 11-hydroxylase (11-OHase) activity in squirrel monkeys and in two representative Old World species (cynomolgus and rhesus macaques) in an effort to explain these elevated plasma glucocorticoid and mineralocorticoid levels. The activity of 11-OHase was 5-fold higher in the squirrel monkey than in the Old World species tested. Calculated 11-OHase Vmax was different in the squirrel monkey and the cynomolgus. However, the Km values were similar in the New World primate when compared to cynomolgus. The ability of metyrapone to block 11-OHase was less in the former than in the latter. The data are consistent with the hypothesis that the squirrel monkey adrenal cortex possesses an increased number of 11-hydroxylase enzyme units compared to that of Old World primate species, and is therefore more efficient in producing cortisol. This difference in 11-OHase activity in the squirrel monkey, in addition to other previously reported adrenal steroidogenic enzyme alterations, may be adaptive in nature, favoring increased cortisol and aldosterone production in this and possibly other New World primate species.

New evidence for a direct effect of prolactin on rat adrenal steroidogenesis.

The direct effect of prolactin on rat adrenal steroidogenic enzyme activity was evaluated by measuring plasma and adrenal cytosol steroid levels and adrenal microsomal 3B-hydroxysteroid dehydrogenase/isomerase (3B-HSD), 21 hydroxylase (21-OHase) and mitochondrial 11-hydroxylase (11-OHase) after in vivo administration of purified rat prolactin (rPRL) to adult, female Sprague-Dawley rats. Animals were ovariectomized, hypophysectomized and replaced with ACTH. Two days after surgery rPRL was administered i.p. at doses of 1.0, 10.0 and 100.0 micrograms (micrograms) every 4 hours for 5 days to experimental animals. Control rats received vehicle injections. All rats were sacrificed by decapitation and blood and adrenal glands collected. The adrenals were pooled into each rPRL dose group and mitochondria, microsomes and cytosol prepared from each pool. The activities of 3B-HSD, 21-OHase and 11-OHase were measured using as substrates 14C-dehydroepiandrosterone, 14C-progesterone and 14C-deoxycorticosterone, respectively. Plasma prolactin levels rose from 9.9 +/- 2.5 ng/ml in the control animals to 166.0 +/- 37.7 ng/ml (p less than 0.001) in the 100 micrograms rPRL dose group. Plasma corticosterone levels were not statistically different in the experimental groups when compared to controls. However, adrenal weight was increased in the high dose rPRL group (34.9 +/- 0.9 mg vs 41.9 +/- 1.2 mg, p less than 0.025). Hyperprolactinemia did not influence microsomal 3B-HSD or mitochondrial 11-OHase activities but was associated with a dose dependent decrease in microsomal 21-OHase activity when compared to controls (p less than 0.001). Adrenal cytosol progesterone levels increased with increasing rPRL dose consistent with a 21-OHase block during hyperprolactinemia. These data suggest that prolactin has a direct effect on rat adrenal 21-OHase in vivo.