Endocrine pathogenesis of postweaning anestrus in swine: response of the persistently anestrous sow to hormonal stimuli.

The endocrine function of the individual components of the hypothalamo-hypophyseal-ovarian axis of the postweaning anestrous sow was evaluated by monitoring the sow's response to exogenous estradiol, gonadotropin releasing hormone (GnRH), and gonadotropins. Sows (4 to 6/group) not returning to estrus by 42.8 +/- 3.1 days after weaning were assigned to 1 of the following treatments: 10 micrograms of estradiol benzoate (EB)/kg of body weight; 200 micrograms of GnRH, 1,000 IU of pregnant mare's serum gonadotropin (PMSG); 1,000 IU of human chorionic gonadotropin (HCG); or 4 ml of saline solution plus 2 ml of corn oil. A preovulatory-like surge of luteinizing hormone [(LH) greater than 12 hours in duration] was observed in all weaned sows treated with EB. All EB-treated sows exhibited estrus and ovulated but none conceived. Sows given GnRH had transiently increased (less than 3 hours) LH concentrations that were not associated with estrus or ovulation. Treatment with PMSG caused an increase in peripheral concentrations of 17 beta-estradiol that was followed by an LH surge, estrus, ovulation, and conception. Treatment with HCG caused an increase in circulating concentrations of 17 beta-estradiol that was accompanied by a surge of LH in some sows and ovulation in all sows. Not all sows treated with HCG exhibited estrous behavior, but conception occurred in 2 of 3 sows that were mated at estrus. None of the sows treated with saline plus corn oil had consistent changes in circulatory concentrations of 17 beta-estradiol or LH and none exhibited estrus or ovulated.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrous behavior and circadian discharge of luteinizing hormone in the prepubertal gilt in response to exogenous estrogen.

The influence of varying doses of estradiol benzoate (EB) on the induction of estrus and luteinizing hormone (LH) discharge was studied in crossbred prepubertal gilts of 135 to 150 days of age. Five gilts were assigned randomly to each of 6 groups and treated with 0, 10, 20, 100 or 200 micrograms EB/kg body weight (BW) at 1200 h or with 10 micrograms/kg at 2400 h. The characteristics of the estrous and endocrine responses of the prepubertal gilts to EB were compared to the responses of 4 ovariectomized, adult gilts treated with EB. Dose of EB administered to prepubertal gilts had no influence on the interval from injection to estrus. Amount of EB administered, however, was correlated positively (r = 0.82, P less than 0.001) with the duration of estrus. Increasing the dose of EB tended to increase (0.05 less than P less than 0.10) the proportion of prepubertal gilts in estrus. Ovariectomized adult gilts treated with 10 micrograms EB/kg BW were in estrus for a duration similar to that of prepubertal gilts treated with that dose of EB. All doses of EB induced at least one surge of LH in each prepubertal gilt. As the dose of EB was increased, a greater proportion of prepubertal gilts showed 2 surges of LH at a 24-h interval. Dose had no influence either on the magnitude or the duration of LH surges. In all gilts, whether prepubertal or mature, surges of LH occurred at either 2400 or 0600 h. Thus, gilts treated with EB at either 2400 or 1200 h were asynchronous with respect to time after treatment until LH peak but were synchronous relative to the time during the day of LH surge. Ovariectomized adult gilts treated with EB had a single surge of LH that was similar in magnitude and duration to the first surge of LH observed in prepubertal gilts.(ABSTRACT TRUNCATED AT 400 WORDS)

Relaxin concentrations in pig plasma following the administration of prostaglandin F2alpha during late pregnancy.

Concentrations of relaxin in peripheral plasma were measured following the injection of 10 mg of PGF2alpha to pregnant sows on day 112 of gestation. The mean concentrations of relaxin before injection of PGF2alpha were less than 13 ng/ml. Relaxin concentrations increased sharply to a mean of 104 ng/ml by 45 min following injection of PGF2alpha and then fell rapidly to a mean of 40 ng/ml 4 h later. Following this initial peak of relaxin, there was a gradual rise and fall of relaxin concentrations during the day preceding parturition. The levels of relaxin during this period were also influenced by PGF2alpha administration since the mean levels of relaxin were significantly lower from the 22nd through the 10th h before parturition in pigs given PGF2alpha, than in pigs given saline.

Radioimmunoassay of plasma relaxin levels throughout pregnancy and at parturition in the pig.

Relaxin concentrations in peripheral plasma have been measured throughout pregnancy and immediately following parturition in the pig by radioimmunoassay. Gestation ranged from 114-117 days. Relaxin concentrations remained below 2 ng/ml during the first 100 days of pregnancy and then rose gradually to a mean of 11.9 ng/ml by 3 days before parturition. At this time, relaxin levels began to rise more rapidly and over the next 2 days increased to a mean concentration of 44.0 ng/ml by 30 h before parturition. Relaxin concentrations then increased sharply to a mean of 145.6 ng/ml by 14 h before parturition. This maximum was followed be a rapid decrease to a mean of 42.4 ng/ml by 2 h before parturition. At one day following parturition, relaxin levels were less than 1 ng/ml.