Are the short-photoperiod-induced decreases in serum prolactin responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters?

Serum prolactin (PRL) decreases in Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters following short-photoperiod exposure. Both species also exhibit short-photoperiod-induced changes in body and lipid mass, but in opposite directions; Syrian hamsters increase and Siberian hamsters decrease their body weight, changes reflected nearly exclusively in their carcass lipid content. The purpose of these experiments was to determine whether the photoperiod-induced changes in PRL were responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters by using the strategy of experimentally producing serum PRL levels opposite to those normally associated with the photoperiod in which the animals were housed. In long photoperiods serum PRL was reduced to short-day levels by subcutaneous (s.c.) CB-154 (bromoergocryptine, a dopamine agonist) injections. In short photoperiods, serum PRL was elevated to long-day levels in Syrian hamsters by ectopic pituitary explants, and in Siberian hamsters, serum PRL was elevated by chronic s.c. infusions of ovine PRL (oPRL). In both species, manipulations of serum PRL did not affect food intake, carcass composition, or the wet weight of various white and brown adipose tissue pads (WAT and BAT, respectively). Body weight increased in CB-154-treated Syrian hamsters and decreased in Siberian hamsters, an effect partially reversed by coadministration of oPRL in Syrian, but not Siberian, hamsters. Thus, lowering serum PRL to short-day levels in long-day-housed hamsters of both species mimicked the directional change in body weight appropriate for each species when they are exposed to short days. This effect of CB-154 on body weight may be a result of some as yet unidentified effect of dopaminergic stimulation on overall growth since 1) these changes in body weight were not reflected as changes in lipid mass, as occurs naturally following short-day exposure for each species, and 2) neither species exhibited a reciprocal change in body weight when serum PRL was experimentally elevated in short days. Alternatively, it may be that once the energetic responses to short-day exposure have been fully expressed, the ability of PRL to stimulate the target sites of action for PRL for these responses may be decreased. BAT protein content, cytochrome oxidase activity (measures of metabolic growth of this tissue), and retroperitoneal total and specific lipoprotein lipase (LPL) activities were increased by CB-154 treatment in Syrian hamsters.(ABSTRACT TRUNCATED AT 400 WORDS)     

2-bromo-alpha-ergocryptine mesylate (CB-154) inhibits prolactin and luteinizing hormone secretion in the prepubertal female rat

Treatment of immature female rats with 100 micrograms 2-bromo-alpha-ergocryptine mesylate (CB-154) per ml drinking water beginning on Day 30 of age until vaginal opening delayed puberty by 6 days. Rats treated with CB-154 exhibited vaginal opening at 43.3 +/- 0.6 days whereas controls exhibited vaginal opening at 37.9 +/- 0.8 days. Most interestingly, serum levels of luteinizing hormone (LH) and prolactin (PRL) on Days 31-35, determined by a homologous radioimmunoassay were significantly lower in treated rats than in controls. The ovarian concentrations of progesterone (P) and androstenedione (A) were lower in rats treated with CB-154 than in controls; ovarian estradiol (E2) concentrations were low in both groups. Serum levels of P (but not A and E2) were reduced on Days 31-35 of the treatment period. Cessation of the CB-154 treatment on the morning of Day 35 returned the onset of puberty to normal values; steroid and gonadotropin levels also returned to normal values within 2 days after removal of the CB-154 from the drinking water. Near the time of onset of puberty, serum levels of LH in rats treated with CB-154 returned to control values. These data indicate that in the female rat the delay in puberty induced by CB-154 might be due to a reduction in the secretion of LH, especially since the onset of delayed puberty in rats treated with CB-154 correlates with an increase in the serum level of LH. Further studies are needed to elucidate the specific effects of hypoprolactinemia on ovarian function and the onset of puberty in the rat.     

Prolactin modulation of the maternal-like behavior displayed by juvenile rats

Reports of elevated prolactin (Prl) levels in juvenile rats of the same strain and approximate age, together with the established role of Prl in maternal behavior in adult female rats, prompted us to examine the possible involvement of Prl in the expression of maternal-like behavior in juvenile Sprague-Dawley males and females. Experiment 1 showed that at 25 days of age both sexes exhibited a rapid onset of full maternal behavior (FMB), with males (median = 2.0 days) responding significantly more quickly than females (median = 4.0 days). Moreover, blood sampled for Prl revealed that males had significantly higher levels of circulating Prl than females, (21.0 vs 10.4 ng/ml, respectively). In Experiment 2, CB-154 treatment significantly delayed the onset of FMB in males only, causing latencies to increase to 5.0 days vs 2.0 days for Controls. Female latencies were unaffected by CB-154, 7.0 and 7.5 days for CB-154 and Control groups, respectively. A second set of both male and female juveniles was treated with either CB-154 or vehicle. CB-154 reduced Prl levels in both sexes. In the Controls, the sex difference in Prl levels (males greater than females) was again evident. In Experiment 3 juvenile males were treated with either ovine Prl (0.5 mg) + CB-154, CB-154 + Vehicle, or Vehicle + Vehicle and tested for FMB. Males treated with Prl + CB-154 required 3.0 days to exhibit FMB, significantly faster than CB-154 + Vehicle males which responded in 8.0 days. The response of Vehicle + Vehicle males was intermediate, with a latency of 5.0 days. These results provide support for the idea that Prl is involved in the maternal-like responsiveness shown by 25 day old juvenile males, but that in females a maturational factor may have prevented both heightened responsiveness to pups by 25 days of age and sensitivity to the Prl releasing mechanism(s)/Prl feedback involved in the exhibition of maternal behavior.     

Serum prolactin levels of rats under continuous estrogen stimulation and 2 Br-alpha-ergocryptine (CB-154) injection.

The ability of 2 Br-alpha-ergocryptine (CB-154) to suppress serum prolactin levels was examined in animals under the influence of continuous estrogen stimulation. A single injection of polyestradiol phosphate (Estradurin) once every 21 days produced a constant elevation of serum prolactin. The simultaneous administration of 1 mg/day of CB-154 to estrogenized animals suppressed serum prolactin levels below that of Estradurin alone but the levels were significantly greater than those of animals receiving CB-154 alone. It was suggested that, while CB-154 prevents the release of prolactin, estrogen stimulates prolactin synthesis despite the block of its release. Ether anesthesia may be capable of partially overriding the block of CB-154 and released the stored hormone from the gland.     

Photoperiodic regulation of glutamatergic stimulation of secretion of luteinizing hormone in male Syrian hamsters.

It has been suggested that changes in endogenous glutamatergic stimulation of secretion of luteinizing hormone (LH) induced by photoperiod play a role in regulating seasonal cycles of reproductive activity. The aim of this study was to test the hypothesis that the glutamatergic control of the secretion of LH in the male Syrian hamster is sensitive to photoperiod, by determining whether the glutamate agonist N-methyl-D-aspartate (NMDA) could stimulate LH secretion in this species and, if so, to determine whether the response varied among animals exposed to different daylengths. In the first experiment, adult male hamsters were housed in either short day (8 h light: 16 h dark) for 6 weeks to induce testicular regression, or long days (16 h light: 8 h dark) to maintain testicular function, and the effects of systemic administration of NMDA on serum LH concentrations were determined. In the short-day hamsters, all s.c. doses of NMDA (25-75 mg kg-1 body weight) produced a robust rise in serum LH concentrations within 15 min. In the long-day hamsters, basal LH concentrations were higher than in short-day hamsters, but only the highest dose of NMDA produced a significant increase in LH concentrations, and the magnitude of this increment was less than those observed in short days. In hamsters in long days, the low doses of NMDA that did not significantly alter LH concentrations nevertheless significantly suppressed serum prolactin concentrations, demonstrating the efficacy of the drug. In hamsters in short days, serum prolactin concentrations were at the limit of detection of the assay, so no inhibitory effect of NMDA on prolactin secretion could be determined on this photoperiod. In the second experiment, the effects of a fixed dose of NMDA (50 mg kg-1 body weight) was tested at intervals in hamsters exposed to short days for a prolonged period such that their testes initially regressed, but then became scotorefractory and testicular recrudescence occurred. After 6 and 12 weeks in short days, NMDA stimulated LH secretion. However, after 24 weeks in short days when testicular recrudescence was complete, the response to NMDA was lost. A third experiment determined whether the reduced response to NMDA in hamsters on long days relative to those in short days might result from higher concentrations of circulating testosterone. Hamsters in long days were castrated to remove the influence of gonadal feedback, and the response to NMDA tested 3 weeks later when endogenous LH concentrations had risen to levels characteristic of the chronically castrated condition.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of photoperiod on the size of the Leydig cell population and the rate of recruitment of Leydig cells in adult Syrian hamsters

The number of Leydig cells was determined by stereologic procedures in adult Syrian hamsters housed in long days (14L:10D) to maintain testicular activity (active), in short days (5L:19D) for 12-13 wk to induce testicular regression (photoperiod-induced regressed), or in short days for a period of 21 wk or more to allow spontaneous gonadal recrudescence (spontaneously recrudesced). Testes were removed, sliced, fixed, embedded in Epon 812, and observed by bright-field microscopy. Testicular and seminal vesicle weights, plasma testosterone concentration, total Leydig cell volume per testis, and volume of single Leydig cell were greater (p less than 0.01) in active and recrudesced animals than in regressed animals. The density of Leydig cells was greater in the regressed testes, but the total number per testis was not influenced by photoperiod. In Experiment 2, the rate of recruitment of Leydig cells was determined in 5 adult hamsters exposed to long days (active) or 5 hamsters whose testes were regressed by exposure of animals to short days for 13 wk followed by long-day exposure to initiate testicular growth (photoperiod-induced recrudescing). Hamsters were injected for 3 days/wk for 3 wk with tritiated thymidine, 0.5 or 1 microCi/g body weight. Testes were fixed and tissues prepared, as above, and processed for autoradiography. Again, the photoperiod did not influence the number of Leydig cells per testis. Labeling of Leydig cell nuclei revealed that recruitment of new Leydig cells occurred at approximately 1.3% per day in recrudescing testes but also occurred at approximately 0.6% per day in active testes. Without change in the total number of Leydig cells, new Leydig cells were added continually to the existing population in adult hamsters with either recrudescing or active testes.     

Humoral factors and nonspecific immune suppression in Syrian hamsters infected with Leishmania donovani

Leishmania donovani produces progressive wasting and ultimately fatal visceral leishmaniasis in Syrian hamsters and provides an excellent model of progressive disease in humans. Experimentally infected hamsters were used to investigate the development of nonspecific immune suppression during visceral leishmaniasis and its association with humoral factors and wasting. At 2 wk all infected hamsters had developed antibody against a 59-kDa parasite antigen not recognized by sera of control hamsters. By 4 wk, strong antibody responses were noted against antigens of 26, 35, 46, 69, 107, and 120 kDa. No additional antigen was recognized at 6 or 8 wk or in hamsters treated with high doses of a pentavalent antimonial (stibogluconate sodium, 100 mg/kg/day for 5 days). Weight loss was first noted in infected hamsters at 8 wk. No difference in splenic lymphocyte proliferation in response to concanavalin A (Con A) was noted at 2 wk, but by 6 wk infected animals had only 20% of the Con A response of controls, and by 8 wk only 13%. Furthermore, incubation of splenic lymphocytes from uninfected control animals with 5% fetal calf serum and 5% serum from infected hamsters obtained at 4, 6, or 8 wk suppressed Con A responses by 50%, 99%, and 100%, respectively. Spleen cells from drug-treated animals exhibited no suppression of Con A responses when incubated with 5% autologous serum, but there was profound suppression when they were incubated with 5% autologous serum obtained during the acute phase of infection. Humoral factors, but not wasting, contributed to the suppression of lymphocyte responses.     

Role of testosterone levels and of hypophysis in the HCG-induced modifications of the 7 alpha-hydroxylation and 5 alpha-reduction processes in incubated rat testes

The role of a direct or a hypophysis-mediated influence of increased testosterone levels in the effects of a long-term high-dose HCG administration (10 IU/day) upon the 7 alpha-hydroxylation and 5 alpha-reduction activities of incubated testes of mature rats was investigated. Administration of high doses of HCG to hypophysectomized rats resulted in the same metabolic changes as in normal rats, namely, a large decrease in the 7 alpha-hydroxylation and an increase in the 5 alpha-reduction processes. Administration of testosterone-propionate (0.2 mg and 20 mg/day) for several days to hypophysectomized rats and to normal rats receiving and substitutive dose of 1 IU HCG/day, did not modify the testicular metabolization pattern. These findings indicate that the decrease in testicular 7 alpha-hydroxylation activity induced by long-term administration of high doses of HCG is probably not mediated by the hypophysis nor by the extracellular testosterone levels.     

Timing of meiotic stages in oocytes of the Syrian hamster (Mesocricetus auratus) and analysis of induced chromosome aberrations

Summary The stages of maturation of oocytes (meiotic stages) in adult Syrian hamsters (Mesocricetus auratus) have been timed following superovulation treatment. Timing and superovulation were induced by an injection of pregnant mares' serum on the first morning of the estrus cycle, followed by injection of human chorionic gonadotropin (HCG) in the evening of the fourth day. The oocytes completed the prophase of the first maturation division 3 h after the injection of HCG. Ovulation began 91/2h after the injection. A method of analysis of metaphase II chromosomes of Syrian hamster oocytes 16h after injection of HCG is described. This method seems to be appropriate for the examination of the induction of genetic defects during oogenesis. Female hamsters were treated with 2,3,5-triethyleneimono-benzoquione-1,4. The induced chromosome aberrations were analysed. Dosis-dependent response could be demonstrated.     

Potentiation by epidermal growth factor of the in vitro HCG stimulation of testicular steroidogenesis in hamsters.

Epidermal Growth Factor (EGF) has been reported to stimulate or inhibit steroidogenesis in murid Leydig cells depending on the experimental conditions used. In the present study, testicular fragments from an adult cricetid rodent, the Syrian hamster, were incubated with various doses of mouse EGF (0-2.0 micrograms/ml media), in the presence or absence of HCG (0-12.5 mlU/ml media). Although EGF alone did not affect in vitro testicular steroidogenesis, it significantly potentiated the HCG-induced elevation of the accumulation of testosterone and 17-hydroxyprogesterone in the media. In contrast, the effect of HCG on media progesterone concentration was not affected by EGF. Since in the Syrian hamster intracellular calcium loading functions as a gonadotropic stimulus, the present results could be a consequence of the EGF-induced increase in cellular calcium levels.     

Interspecies differences in testicular LH receptors and in vitro testosterone production among rodents

Testes from rats, mice and hamsters were incubated for 4 h with 0, 3.125 or 12.5 mIU hCG/ml. The LH receptor concentration in incubated testes of rats and mice was higher than that observed in hamsters. Testosterone levels in incubation media were significantly different among species (mice greater than rats greater than hamsters). During the incubation, hCG caused an increase in testosterone levels in all three species, but produced no significant changes in LH receptor concentration. Furthermore, a correlation between LH receptor concentration and testosterone only in hamsters is observed. The efficiency of the LH receptor-steroidogenesis interaction was estimated from the ratio of testosterone levels to receptor concentration under basal conditions and was found to differ among species (mice greater than hamster greater than rats). The levels of PGE and PGF in incubation media were higher in mice than in rats or hamsters, and hCG did not alter prostaglandin levels in any of the species. The present results indicate that acute in vitro hCG stimulation of testosterone synthesis does not involve appreciable changes in testicular LH receptor levels.     

Effect of oxytetracycline and erythromycin on Syrian hamsters after intratracheal infection with Mycoplasma pneumoniae

Male Syrian hamsters were infected intratracheally with Mycoplasma pneumoniae and treated here after for ten days with either OTC or erythromycin. The purpose of this study was to investigate whether there exists a relation between the persistence of M. pneumoniae in the lungs and the infection dose respectively the days passed after infection before starting treatment with antibiotics. The influence of antibiotic therapy on the immune response of the hamsters was also investigated.     

Partial maintenance of testes and accessory organs in blinded hamsters by homoplastic anterior pituitary grafts or exogenous prolactin

When blinded, golden Syrian hamsters undergo marked gonadal atrophy. This phenomenon is prevented by pinealectomy. The mechanisms involved in this pineal-mediated response were investigated through either the transplantation of pituitary homografts or treatment of blinded, male hamsters with exogenous prolactin. It was found that anterior pituitary homografts placed beneath the kidney capsule on the day of bilateral optic enucleation partially maintained testicular and accessory organ weights. Serum prolactin levels were reduced in blinded animals below that of intact controls. On the other hand, blinded hamsters bearing anterior pituitary homografts showed serum prolactin levels comparable to those of intact controls. In other experiments, the injection of either 3.2 or 6.4 I.U. of ovine prolactin/hamster/ day for a period up to seven weeks partially inhibited the atrophy of testes and accessory organ weights in blinded hamsters. These data suggest a possible role for prolactin in the pineal-mediated atrophic response to light deprivation.     

Short days and exogenous melatonin increase aggression of male Syrian hamsters (Mesocricetus auratus)

Many nontropical rodent species rely on photoperiod as a primary cue to coordinate seasonally appropriate changes in physiology and behavior. Among these changes, some species of rodents demonstrate increased aggression in short, "winter-like" compared with long "summer-like" day lengths. The precise neuroendocrine mechanisms mediating changes in aggression, however, remain largely unknown. The goal of the present study was to examine the effects of photoperiod and exogenous melatonin on resident-intruder aggression in male Syrian hamsters (Mesocricetus auratus). In Experiment 1, male Syrian hamsters were housed in long (LD 14:10) or short (LD 10:14) days for 10 weeks. In Experiment 2, hamsters were housed in long days and half of the animals were given daily subcutaneous melatonin injections (15 microg/day in 0.1 ml saline) 2 h before lights out for 10 consecutive days to simulate a short-day pattern of melatonin secretion, while the remaining animals received injections of the vehicle alone. Animals in both experiments were then tested using a resident-intruder model of aggression and the number of attacks, duration of attacks, and latency to initial attack were recorded. In Experiment 1, short-day hamsters underwent gonadal regression and displayed increased aggression compared with long-day animals. In Experiment 2, melatonin treatment also increased aggression compared with control hamsters without affecting circulating testosterone. Collectively, the results of the present study demonstrate that exposure to short days or short day-like patterns of melatonin increase aggression in male Syrian hamsters. In addition, these results suggest that photoperiodic changes in aggression provide an important, ecologically relevant model with which to study the neuroendocrine mechanisms underlying aggression in rodents.     

Differential effects of bromocriptine treatment on LH release and copulatory behavior in hyperprolactinemic male rats

Hyperprolactinemia (hyperPRL) induced by grafting four pituitary glands under the kidney capsule suppresses copulatory behavior in male rats and sexually naive male mice. In mice sexual experience attenuates the suppressive effects of hyperPRL on mating behavior, thus a comparison of the behavioral consequences of inducing hyperPRL in sexually naive and experienced male rats was undertaken. Hyperprolactinemia had a significant suppressive effect on mating behavior in both groups of animals. Experienced animals showed deficits in all parameters studied except mount frequency and postejaculatory interval, while naive animals differed from respective controls only in mount latency, intromission latency, and intromission frequency. To determine if the inhibition of chronically elevated prolactin (PRL) levels would reverse the suppression of gonadotropin secretion and copulatory behavior in hyperprolactinemic animals, the effects of bromocriptine (CB-154) administration on plasma hormone levels and mating behavior were examined in pituitary-grafted and control rats. Bromocriptine treatment (1 mg/day for 14 days) led to increases in sexual activity in both the sham-operated and grafted animals. In the grafted animals, plasma PRL was reduced and plasma LH significantly increased in the CB-154-treated animals when compared to oil-treated controls. In sham-operated animals, CB-154 produced no significant changes in plasma LH or FSH despite the suppressed PRL levels. These results indicate that (1) hyperPRL induced by pituitary grafts can cause deficits in mating behavior in male rats despite previous sexual experience, and (2) while CB-154 may be acting through other mechanisms to stimulate copulatory behavior, the reduction of chronically elevated PRL levels due to CB-154 treatment is responsible for reversal of the suppressive effects of hyperPRL on LH secretion.     

Basal and HCG-stimulated testosterone production by interstitial cells of the Mongolian gerbil (Meriones unguiculatus)--I. Influence of preincubation length, medium composition and temperature

In the absence of HCG, production of testosterone by whole testes superfused in vitro was quite constant during the 5-hr superfusion period. Addition of 23-184 mIU/ml HCG caused a significant increase of testosterone production which was apparent from 30 min after start of superfusion. Basal and HCG-stimulated testosterone production by whole testes was significantly higher (400, 1950 ng/testis/5 hr, without and with 100 mIU HCG) than by isolated cells (200, 1350 ng/testis/5 hr). Incubation of isolated interstitial cells in medium 199 supplemented with fetal calf serum (FCS), (N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid, HEPES) and 3-isobutyl-methylxanthine (MIX), and in medium 199 without FCS, HEPES or MIX, gave similar testosterone responses. While centrifugation at 8000 g for 2 min drastically diminished testosterone formation by isolated interstitial cells, production was similar by cells incubated in either 0.5, 1.0 or 1.5 ml medium. A significant decrease of testosterone synthesis by isolated interstitial cells was found when cells were stored at 4 degrees C for 2 days and then were incubated at 35 degrees C for 6 hr without or with 1-1000 microIU HCG. While isolated interstitial cells incubated at 5 degrees C did not produce testosterone at all, testosterone production increased to 49.5 +/- 3.9 ng/10(5) cells (30 degrees C) and 24.1 +/- 1.1 ng/10(5) cells (40 degrees C), respectively. HCG-stimulated testosterone production was maximal when interstitial cells were incubated at 34 degrees C.     

The lack of a physiologic effect of the stress-induced decrease of the proestrous prolactin surge in the rat

Experiments were performed to determine whether the restraint stress-induced decrease in the proestrous prolactin (PRL) surge blocked luteolysis of the corpora lutea (CL), affected ovulation, or prevented the induction of pregnancy/pseudopregnancy in the next cycle. In all experiments rats were either stressed on proestrus and estrus, administered daily sc injections of 1 mg/day of 2-Br-alpha-ergocryptine (CB-154) for 4 days starting on diestrus II or not treated. In one experiment animals were sampled on the afternoon of proestrus to determine the effect of restraint stress on plasma PRL values and sacrificed on the morning of proestrus in the next cycle. Ovaries were removed, weighed, fixed and examined for number of CL. Restraint stress resulted in a significant increase in ovarian weight when compared to controls; CB-154 resulted in significant increases in ovarian weight when compared to stress and control animals. However, only CB-154-treated animals had a significant increase in the number of CL when compared to controls. In another experiment, animals were sacrificed on estrus of the next cycle and the oviducts examined for the number of ova. There were no differences among groups. In the final experiment, animals were placed with males of proven fertility on proestrus of the next cycle and examined for evidence of sperm in the vaginal lavage and/or vaginal plugs. CB-154 prevented the induction of pregnancy or pseudopregnancy due to a carry over effect of the drug on PRL surges. Restraint stress had no significant effect on the induction of pregnancy or pseudopregnancy. We conclude that there is no physiological significance to the stress-induced decrease of the proestrous PRL surge with respect to ovarian function or fertility.     

Intraperitoneal injection of chloral hydrate causes intra-abdominal adhesions and unilateral testicular atrophy in golden Syrian hamsters.

We investigated the reason for the high mortality we had observed in hypophysectomized-orchidectomized Golden Syrian hamsters that were anesthetized with intraperitoneal (i.p.) injections of chloral hydrate (CH). Intact male Golden Syrian hamsters were injected intraperitoneally with 0.1cc/100g BW of a 35% solution of CH, a 35% solution of sodium chloride, or double-distilled water. Equal numbers of hamsters in each group were injected on the right or left side of the abdomen. Within 10 days, 35% of the CH-injected hamsters were dead or had to be euthanized. Autopsy revealed severe peritonitis and adynamic ileus. CH-injected hamsters that survived gained weight at a rate similar to that of the controls. All surviving hamsters were killed 18 days after the injections. Among the surviving CH-injected hamsters, 84.6% had intra-abdominal adhesions, 61.5% had unilateral testicular atrophy, and 53.8% had a yellowish necrotic mass in the epididymal fat pad (EFP). All the lesions occurred on the side that was injected. The atrophied testes had been rendered cryptorchid due to involvement with intra-abdominal adhesions. In the water-treated controls, there were no abnormalities; whereas, in the saline controls, 75% had a mass in the EFP. Histology of the EFP mass was similar in hamsters injected with CH or hypertonic saline and suggested a diagnosis of fat necrosis. The results suggest that the mortality, the intra-abdominal adhesions, and the unilateral cryptorchidism were caused by a single i.p. injection of CH, but the fat necrosis in the EFP was probably caused by high concentrations of salt. The results further suggest that high concentrations of CH should not be injected intraperitoneally for anesthesia in chronic studies, particularly of the male reproductive system.     

Response of lutropin (LH) and follitropin (FSH) to the administration of gonadoliberin (GnRH) in pregnant and post-partum cattle including experiments with prolactin suppression

GnRH (250 μg) was administered intravenously in a total of 121 experiments carried out on 21 cows during the period from 180 days ante (ap) to 50 days post partum (pp). Additionally in one group of animals prolactin secretion was inhibited after parturition by means of 3 intramuscular injections of 150 mg Bromocryptine (CB-154) on days 1, 4 and 7 pp. LH response (peak height, area under the dose response curve) was about the same from 150 to 60 days ap, then decreased significantly towards parturition and was lowest during the first 6 days post partum. At a later time the Lh response was more pronounced than during pregnancy. The FSH response decreased significantly during the last 9 days ap, remained low during the frist 6 days pp and increased thereafter. There was no significant influence of prolactin inhibition on LH and FSH values (except for the total FSH released on day 50 pp). Whereas in all GnRH treated animals pronounced pituitary gonadotropin responsiveness was measurable (except during the period around parturition), the variation of the LH response pp was much higher than ap. The LH results gave some indication of the wide range of response pattern for this hormone after parturition which might be one reason for the individuality in the initiation of a new estrous cycle post partum in cattle.     

Immunohistochemical localization of prolactin in functioning and regressing corpus luteum of pituitary autotransplanted rats

In an attempt to shed light on the intimate mechanism by which prolactin (PRL) switches from supporting corpus luteum (CL) progesterone secretion (P) to promote structural regression of the CL, day 2 (metestrous) autopituitary transplanted (APTr) rats were used. In APTr rats the CL is under the only control of PRL since an almost complete absence of LH and FSH exist. The experimental group was given bromocriptine (CB-154: 0.4 mg/day) on days 12, 13 and 14 of the cycle and 0.25 ml of ethanol from day 15 to day 21. The control group was given CB-154 from day 12 to day 21. Rats were hemiovariectomized on day 12 to assess the morphological characteristics of the active CL. PRL and P were determined by RIA on days 12, 15 and 22. On day 12, both PRL and P levels were higher than 80 ng/ml (luteotrophic action of PRL). On day 15, due to treatment with CB-154, the levels of both hormones had fallen below 7 ng/ml (functional luteolysis). On day 22, PRL levels were again high (greater than 50 ng/ml) in the shortly CB-154-treated rats and low (less than 5 ng/ml) in the controls; the P levels were lower than 5 ng/ml in both groups. PRL-induced structural luteolysis in the experimental group (hyperprolactinemic) was assessed by the structural characteristics and by the CL weight loss on day 22 in comparison with that exhibited by control rats. The immunohistochemical staining of both endogenous and total PRL in the lutein cells showed that the internalization of PRL is not modified by the functional state of the CL, nevertheless the intracellular redistribution of the internalized hormone varied in relation with the PRL action on the CL (luteotrophic, day 12 vs luteolytic, day 22). These results seem to indicate that intracellular mechanisms rather than receptor content determine CL response to PRL.