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Search for other papers by G. M. NEHER in
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Search for other papers by M. X. ZARROW in
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SUMMARY
The Hooker-Forbes assay was employed to determine the concentration of free progestin in the serum of ewes during various stages of the reproductive cycle.
During the oestrous cycle, the concentration varied from 0\m=.\3 to 2μg/ml. at oestrus to 6μg in the luteal phase. During pregnancy, the level of progestin rose from 1 to 2 μg/ml. at mating to a peak of 8–12 μg/ml. at parturition. The concentration of progestin showed a plateau at a level of 6–8 μg from the 40th to the 100th day of pregnancy. A second rise occurred at about the 120th day of pregnancy.
In all sheep parturition took place prior to the drop in serum progestin. By the 10th day post-partum, however, the concentration of the hormone declined to 1 or 2 μg/ml. and remained at this level throughout lactation. Removal of the ovaries between the 66th and 114th day of gestation had no effect on the level of progestin in the blood of five ewes. The pregnancies remained unaffected, and the concentration of progestin increased in a manner comparable to that seen in pregnant sheep with intact ovaries. It is suggested that the placenta is the major source of progestin during the last two trimesters of pregnancy in the sheep.
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Search for other papers by J. H. CLARK in
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SUMMARY
Ovulation was blocked in pregnant mare serum-treated immature rats by treatment with chlorpromazine. Reflex ovulation and hence luteinizing hormone release was induced by three procedures: (a) placing male rats with the treated females overnight, (b) mechanical stimulation of the vagina and cervix with a glass rod, and (c) electrical stimulation of the uterine cervix. Mating or mechanical stimulation induced ovulation in 77 and 82% of the rats, respectively. Electrical stimulation was least effective, causing ovulation in only 50%. The average number of ova released and the percentage of rats ovulating was found to be a function of the amount of mechanical stimulation with the glass rod. Pelvic neurotomy abolished the reflex ovulatory response. The stronger response obtained by coitus or mechanical stimuli indicated the possibility of receptor sites in the vaginal wall. This assumption was supported by the finding of penile spines in the rat. A survey of the literature indicates that penile spines are present in a variety of mammalian orders including the primates. The evolutionary relationships and implications of the existence of penile spines and reflex ovulation are discussed. It is suggested that man, like the rat and probably other species which ovulate spontaneously, also has the ability to ovulate after stimulation of the vaginal tract.
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Search for other papers by J. H. CLARK in
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SUMMARY
The ovarian cholesterol depletion assay for luteinizing hormone (LH) was investigated in the untreated immature rat. The prepubertal rat is a satisfactory animal to use in this assay because the diurnal rhythm in ovarian cholesterol is not present until puberty. A dose-response curve was obtained between 2·5 and 10·0 μ LH and the average lambda was 0·17. The assay was specific for LH; the presence of other pituitary hormones had no significant effect on the relative potency of NIH-LH preparations. The assay is probably not sensitive enough for untreated plasma but had excellent reproducibility and is easily performed.
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Search for other papers by M. X. ZARROW in
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SUMMARY
An antibody to relaxin that combined with the hormone in immunodiffusion and haemagglutination tests was produced in rabbits. The antibody quantitatively inhibited the interpubic ligament-response to relaxin in oestrogen-primed immature female mice and partially inhibited the separation of the pubic bones at the symphysis pubis in the parturient mouse.
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Search for other papers by J. A. McCLINTOCK in
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SUMMARY
An antibody to relaxin labelled with 131I was injected into pregnant mice and rats. It was found to be localized in the ovaries, placenta, and uterus of the mouse. The localization in the ovary and placenta was apparent on day 10 of pregnancy, increased markedly to a plateau on days 14–15, and fell at parturition. In the uterus accumulation of 131I anti-relaxin antibody rose to a much smaller degree than in the other two tissues and fell before parturition. Analysis of rat tissues during pregnancy indicated a localization of the labelled antibody in the ovary, placenta, cervix and mammary gland. The localization of the antibody was competitively inhibited by simultaneous injection or preincubation with relaxin. The localized antibody was competitively extracted by saline solutions containing relaxin but not by saline alone.
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Search for other papers by E. D. WILSON in
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SUMMARY
Marked pubic separation, comparable to that in the guinea-pig, mouse and deermouse, was observed to occur in the Skomer bank vole towards the end of gestation when the pubic gap measured 4–5 mm. Ovariectomized Skomer voles treated with oestradiol showed a pubic separation of 0·8–0·9 mm., while treatment with oestradiol and relaxin caused a separation of 2·5–4·6 mm. Relaxin alone had no effect.
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Search for other papers by K. BROWN-GRANT in
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SUMMARY
The effect of age and dose of a single injection of pregnant mare serum gonadotrophin (PMS) on spontaneous ovulation in immature Wistar rats is described. Ovulation could be induced by human chorionic gonadotrophin (HCG) at least 6 days before it occurred when pregnant mare serum gonadotrophin alone was given. Chlorpromazine was shown to block pregnant mare serum gonadotrophin-induced ovulation at a dose level (0·25 mg. in a 60 g. rat) which has no effect on the ovulatory response to human chorionic gonadotrophin. Higher doses interfered with the action of injected human chorionic gonadotrophin. Ovulation could be induced in the chlorpromazine-blocked animals by the systemic injection of an extract of bovine median eminence, but the sensitivity was too low to use this response for an assay method.
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Search for other papers by D. L. QUINN in
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SUMMARY
Superovulation can be induced in the immature rat by PMS alone or PMS followed by HCG. Treatment with PMS alone caused an initial average response of 2·8 ova at an age of 20 days and a maximum average response of 70·8 ova at age 28. Treatment with PMS and HCG resulted in an initial average response of 0·3 ova at age 18 days and an average maximum of 61 ova at 22 days of age. A marked drop to approximately 8–10 ova was noted at 45 days of age following both types of treatment. Hypophysectomy revealed that the pituitary gland was necessary for the release of ova following injection of PMS alone. Removal of the pituitary gland as late as 52 hr. after injection of PMS prevented ovulation. Inhibition of ovulation by treatment with dibenamine, SKF-501, atropine and 'Nembutal' following injection of PMS alone led to the concept that superovulation following PMS involves a neural link that is responsible for the endogenous release of LH.
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Search for other papers by JANET DINIUS in
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SUMMARY
The concentration of luteinizing hormone (LH) in the pituitary gland of the 28-day-old female rat increased from a value of 8·0 μequiv./mg fresh anterior pituitary at zero time to 20·1 μg at 51 h after treatment with 30 i.u. pregnant mare serum (PMS). The level then fell to 8·1 μg at 56 h. PMS had no effect on pituitary LH levels in the ovariectomized rat. Three daily injections of 5·0 μg of oestradiol benzoate caused an increase in pituitary LH levels to 16·1 μg at 51 h after the onset of the oestrogen treatment. This value is not significantly different from the level (20·1 μg/mg fresh weight) found in the intact, PMS-treated, immature rat. Uterine weights were also comparable for the two groups. Treatment with lower doses of oestradiol benzoate had no effect on pituitary LH levels and also failed to increase the uterine weight to values comparable with those obtained after PMS treatment. Treatment of 28-day-old, intact, female rats with 2 mg of progesterone at 24 h after the PMS injection resulted in a significant drop in pituitary LH levels.
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Search for other papers by C. M. CHRISTENSON in
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Search for other papers by M. X. ZARROW in
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SUMMARY
Pheromonal facilitation of pregnant mare serum gonadotrophin (PMSG)-induced ovulation was compared in four strains of immature mice after exposure to adult intact males, castrated males, castrated males after treatment with testosterone propionate, or exposure to adult females. Psychobehavioural modification of their response was studied after transferring PMSG-injected females between cages, or after their exposure to either electric foot shock or adverse auditory stimuli. Significant facilitation of the average number of ova released and percentage of mice ovulating was found in females of the strains C3HeB/FeJ and BALB/cJ, but not in strains DBA/2J and C57BL/6J after exposure to adult males. Exposure to castrated males treated with testosterone propionate resulted in a response essentially the same as that to intact males, whereas exposure to adult females inhibited ovulation uniformly in all the strains studied except BALB/cJ. Auditory stimuli prevented this phenomenon in strains C3HeB/FeJ and C57BL/6J, but an obvious facilitation was observed in strains BALB/cJ and DBA/2J. Electric shock facilitated ovulation in strain DBA/2J but not in the other three strains.