A synthetic analogue of meiosis-activating sterol (FF-MAS) is a potent agonist promoting meiotic maturation and preimplantation development of mouse oocytes maturing in vitro.

BACKGROUND: Follicular fluid-meiosis-activating sterol (FF-MAS) is a factor present in the pre-ovulatory follicle during the time of oocyte maturation. In mouse oocytes maturing in vitro, FF-MAS promotes the completion of meiotic maturation to metaphase II (MII) and improves competence to complete the 2-cell stage to blastocyst transition. We produced analogues of FF-MAS and selected three on the basis of potency to promote the resumption of meiosis by mouse oocytes maintained in meiotic arrest by hypoxanthine. The objective of this study was to determine whether these FF-MAS analogues also affect the quality of oocytes maturing in vitro with respect to the completion of meiotic maturation and augmenting the frequency of development to the blastocyst stage after fertilization in vitro. METHODS: Cumulus cell-enclosed oocytes were isolated from the small antral follicles of 18 or 20 day post-natal mice. These oocytes normally have a reduced competence to complete meiotic maturation and preimplantation embryo development. Oocytes were isolated at the germinal vesicle stage and matured in vitro using media supplemented with 0.1% ethanol, 1 micromol/l FF-MAS, or 0.1-10 micromol/l FF-MAS analogues ZK255884 (884), ZK255933 (933) and ZK255991 (991). Oocytes that progressed to MII were fertilized in vitro and the percentage developing to the 2-cell and blastocyst stages was determined. RESULTS: At 1 micromol/l, 991 and 933 increased the portion of oocytes progressing to MII, whereas the lowest dose of 991 and 884 was ineffective. Treatment of maturing oocytes with either 0.1 or 1 micromol/l 933 dramatically increased oocyte competence to complete preimplantation development. CONCLUSIONS: The synthetic analogue of FF-MAS, ZK255933, is a potent agonist that improves the quality of mouse oocytes matured in vitro. This compound may therefore have therapeutic value for treatment of oocytes from women undergoing therapy for infertility owing to poor oocyte quality.

Neuropeptide Y inhibits estrous behavior and stimulates feeding via separate receptors in Syrian hamsters.

Central injections of neuropeptide Y (NPY) increase food intake in Syrian hamsters; however, the effect of NPY on sexual behavior in hamsters is not known nor are the receptor subtypes involved in feeding and sexual behaviors. We demonstrate that NPY inhibits lordosis duration in a dose-related fashion after lateral ventricular injection in ovariectomized, steroid-primed Syrian hamsters. Under the same conditions, we compared the effect of two receptor-differentiating agonists derived from peptide YY (PYY), PYY-(3-36) and [Leu(31),Pro(34)]PYY, on lordosis duration and food intake. PYY-(3-36) produced a 91% reduction in lordosis duration at 0.24 nmol. [Leu(31),Pro(34)]PYY was less potent, producing a reduction in lordosis duration (66%) only at 2.4 nmol. These results suggest NPY effects on estrous behavior are principally mediated by Y2 receptors. PYY-(3-36) and [Leu(31),Pro(34)]PYY stimulated comparable dose-related increases in total food intake (2 h), suggesting Y5 receptors are involved in feeding. The significance of different NPY receptor subtypes controlling estrous and feeding behavior is highlighted by results on expression of Fos immunoreactivity (Fos-IR) elicited by either PYY-(3-36) or [Leu(31),Pro(34)]PYY at a dose of each that differentiated between the two behaviors. Some differences were seen in the distribution of Fos-IR produced by the two peptides. Overall, however, the patterns of expression were similar. Our behavioral and anatomic results suggest that NPY-containing pathways controlling estrous and feeding behavior innervate similar nuclei, with the divergence in pathways controlling the separate behaviors characterized by linkage to different NPY receptor subtypes.

Opioid receptor blockade promotes weight loss and improves the display of sexual behaviors in obese Zucker female rats.

Obese Zucker female rats are hyperphagic, overweight, infertile, and hyporesponsive to the inductive effects of ovarian steroid hormones on sexual behaviors. It has been postulated that endogenous opioid activity may contribute to their obesity and reproductive dysfunction. To test this hypothesis, ovariectomized, adult obese Zucker rats were treated with the opioid receptor antagonist, naltrexone, or saline prior to measurement of steroid-induced sexual behaviors, food intake, and body weight. In estradiol benzoate (EB)-treated rats, naltrexone injection increased the display of sexual receptivity (lordosis quotient, LQ: saline, 11+/-10%; 5 mg/kg naltrexone, 54+/-15%, p < 0.05) and also elicited proceptivity (PRO), which was never observed after saline injection. In EB plus progesterone-treated animals, naltrexone administration enhanced both sexual receptivity and proceptivity (LQ: saline, 17+/-10%; 5 mg/kg naltrexone, 96+/-3%; p < 0.05; PRO: saline, 3.0+/-2.4 bouts/min; 5 mg/kg naltrexone, 45.3+/-12 bouts/min; p < 0.01). Naltrexone injection also decreased 24-h food intake (saline, 24.2+/-0.7 g; 5 mg/kg naltrexone, 17.6+/-1.2 g; p < 0.05) and weight change (saline, +7.3+/-0.8 g; 5 mg/kg naltrexone, -4.5+/-1.4 g, p < 0.01). Morphine treatment blocked these effects of naltrexone on sexual behaviors, food intake, and body weight. These data suggest that endogenous opioids contribute to hyperphagia, obesity, and behavioral hyporesponsiveness to ovarian steroid hormones in obese Zucker rats.

Food restriction neither improves nor exacerbates reproduction in obese female Zucker rats.

Obese female Zucker rats have several reproductive abnormalities, including delayed puberty, abnormal estrous cyclicity, and behavioral hyporesponsiveness to ovarian steroid hormones. To ascertain whether excessive body weight per se causes these reproductive abnormalities, obese Zucker female rats were fed ad lib or were food restricted to match their body weights to those of lean counterparts. Food restriction neither accelerated vaginal opening nor normalized estrous cyclicity in obese female rats. Following ovariectomy, an injection of estradiol benzoate (EB, 15 microg/kg, s.c.) induced extremely low sexual receptivity in all rats, and proceptive behaviors were never observed. After treatment with EB plus progesterone (P, 2 mg/kg, s.c.), lean rats were very receptive (lordosis quotient, LQ = 94 +/- 2%) and proceptive (PRO = 12.5 +/- 2 events/min) while both ad lib-fed and food-restricted obese rats were only marginally receptive and proceptive (LQ= 19 +/- 9%, PRO = 1.8 +/- 0.7 events/min; LQ = 31 +/- 15%, PRO = 4.7 +/- 3 events/min, respectively). A higher progesterone dose (20 mg/kg) elicited vigorous sexual receptivity (LQ = 88-99%) and proceptivity (PRO = 16.5-20.4 events/min) in all EB-treated rats. Adiposity was significantly lower in food-restricted obese rats as compared to ad lib-fed obese rats (36.5 +/- 1.7% vs. 69.4 +/- 2.7%), but greater than that observed in lean rats (24.4 +/- 1.1%). These data suggest that excessive body weight per se does not underlie reproductive abnormalities in obese Zucker rats, but do not rule out the possibility that excessive adiposity may contribute to their infertility.

Intraventricular injection of neuropeptide Y antisera curbs weight gain and feeding, and increases the display of sexual behaviors in obese Zucker female rats.

Obese Zucker rats are hyperphagic, overweight, and infertile. It has been postulated that neuropeptide Y (NPY) overproduction may contribute to obesity and infertility in these animals. To test this hypothesis, ovariectomized, adult obese Zucker rats were implanted with cannulae in the third ventricle and subsequently injected with NPY antisera or normal rabbit sera (NRS) 6, 4 and 2 h before experimental observation. Steroid-treated females injected with NPY antisera were significantly more receptive and were more likely to show proceptive behaviors than after treatment with NRS (e.g., lordosis quotient: NPY antisera, 65.5+/-6.9%; NRS, 30.9+/-11.6%, P < 0.02; 91% displaying proceptivity after NPY antisera injection vs. 36% after NRS, P < 0.03). Injection of NPY antisera also curbed food intake and weight gain (24 h food intake: NPY antisera, 10.5+/-2.1 g; NRS, 20.5+/-1.7 g, P < 0.01; 24 h weight gain: NPY antisera, -5.4+/-2.2 g; NRS, 5.8+/-0.7 g, P < 0.01). Locomotor activity was similar after NRS and NPY antisera treatment (P > 0.5) suggesting that general malaise was not responsible for the effects of NPY antisera on food intake or body weight. These data suggest that endogenous neuropeptide Y contributes to excessive feeding and weight gain, and suppressed reproductive behaviors in obese Zucker female rats.

Similar feeding patterns are induced by perifornical neuropeptide Y injection and by food deprivation.

Although hypothalamic injections of neuropeptide Y (NPY) induce robust feeding, there is little information about the patterns of feeding elicited by this peptide. To reveal these patterns, NPY (0, 8, 24, 78, 235 pmol/10 nl) was injected into the perifornical hypothalamus (PFH) of satiated adult male rats and their subsequent food intake was monitored every minute for 24 h. For comparison, feeding patterns were similarly observed following fasts of 0, 3, 6, 9, 12, and 24 h. The results demonstrated that NPY and food deprivation both produced dose- or deprivation-dependent increases in food intake that were most evident in the first 6 h. The increased intakes induced by NPY were characterized by combinations of increased meal size and frequency, with the predominant effects being increases in the size of and decreased latency to eat the first meal. Similarly, fasting progressively increased food intake by combinations of increased meal size and frequency, with the predominant effects being increases in the size of and decreased latency to eat the first meal. These similarities between NPY-induced and food deprivation-induced feeding are consistent with a stimulatory role for endogenous NPY in deprivation-induced feeding. These findings also suggest that NPY may increase eating by acting on mechanisms of both meal initiation and of meal termination.

Abnormal estrous cyclicity and behavioral hyporesponsiveness to ovarian hormones in genetically obese Zucker female rats.

Obese Zucker female rats are infertile. The present study was designed to assess estrous cyclicity in adult, ovary-intact, lean and obese Zucker rats and to compare reproductive behaviors induced by exogenous steroid hormones in ovariectomized (ovx) lean and obese Zucker rats. The majority (90%) of obese rats had incomplete cycles in comparison with the normal, 4-day cycles displayed by lean Zucker rats. After ovariectomy, all rats were treated with estradiol benzoate (EB, 15-100 micrograms/kg) or EB plus progesterone (P, 2-20 mg/kg), and tested for sexual receptivity and proceptivity (PRO). At the highest EB dose, obese Zucker females displayed lordosis less frequently than lean rats (lordosis quotient, LQ, 8 +/- 6% vs. 32 +/- 13%, respectively). At the lowest doses of EB plus P, lean females were extremely receptive and proceptive (LQ = 93 +/- 4%, PRO = 6.2 +/- 2 bouts/min). Zucker obese females, in contrast, were only slightly receptive (LQ = 26 +/- 11%) and showed less PRO than lean rats (PRO = 2.4 +/- 0.6 bouts/min). Increasing the dose of either EB or P, administered in combination with the lowest dose of the other hormone, produced receptivity and PRO in obese Zucker females that were comparable with those observed in lean rats. Serum estradiol and P levels in ovx obese rats were either equivalent to or higher than those in the ovx lean rats when both were given the same doses of hormones. These data suggest that considerably higher doses and serum concentrations of EB and/or P are required to elicit robust lordosis and PRO in ovx obese Zucker than in lean rats. This behavioral hyporesponsiveness to sex steroid hormones may contribute to infertility in the obese Zucker female rat.