Steroid hormone and luteinizing hormone concentrations in the anestrous sow.
This investigation characterized serum concentrations of luteinizing hormone (LH), estradiol-17 beta (E2), progesterone (P4) and cortisol (C) in anestrous sows. Twenty-two sows that had not returned to estrus within 45 days after weaning (anestrous sows), and ten sows that had returned to estrus within seven days following weaning (cyclic sows) were nonsurgically fitted with indwelling jugular vein cannulae. Blood samples were collected at 6 h intervals for seven days and at 15 min intervals for 8 h on the fifth day after cannulation. Serum LH concentrations were determined in all samples, while C, E2 and P4 levels were quantitated in serum collected at 6 h intervals. Serum P4 concentrations in anestrous sows were consistently less than 0.5 ng/mL, and E2 levels ranged from 10 to 19 pg/mL. Concentrations of LH remained less than 1.0 ng/mL in anestrous sows, whereas a preovulatory LH surge was observed in five of ten cyclic sows. There was a circadian rhythm in mean C levels with C peaks occurring at 0600 or 2400 h and nadir levels observed at 1200 and 1800 h. Few differences in C levels were detected between anestrous and cyclic sows. It was evident that anestrous sows did not exhibit cyclic or predictable variations in steroid hormone concentrations. Unfortunately, the results of this study failed to elucidate the endocrine pathogenesis of the anestrous sow.
Relationships between endogenous gonadotropin-releasing hormone, gonadotropins, and follicular development after weaning in sows.
Two experiments were conducted to examine relationshipsbetween endogenous gonadotropinreleasing hormone (GnRH), concentrations of gonadotropins in the anterior pituitary and blood and ovarian follicular development in weaned sows. In the first experiment, 48 sows were slaughtered during 0 to 5 days after weaning. Because effects of breed, parity, farm and season of slaughter were confounded with day after weaning, data were analyzed solely on the basis of follicular development. Sows were divided into 4 groups based on the size and number of the largest ovarian follicles. Group 1 consisted of 11 sows with largest follicles 14) follicles 5 to 10mm in diameter. Group 4 coniisted of sows (n=12) with follicles>10 mm in diameter. Data from 3 sows that had ovulated were omitted from the analyses.Sows in Groups 1,2, 3 and 4 were killed atm average of 0.7 ± 0.4, 2.5 * 0.2,4.7 ± 0.1 and 4.8 ± 0.2 days after weaning, respectively. Concentrations of GnRH in medial basal hypothalamus (MBH), stalk median eminence (SME) and hypophyseal portal area (HPA) were greater in sows with greater follicular development (Groups 3 and 4). Concentrations of luteinizing hormone (LH) in anterior pituitary (AP) and serum were also greater in Groups 3 and 4. Concentrations of follicle-stimulating hormone (FSH) in AP and serum were not significantly different among groups. In the second experiment, 27 second parity Duroc sows were slaughtered 0, 60 or 96 h after weaning (9 sows per group). Concentrations of both LH and FSH in serum samples obtained at 6-h intervals from weaning to slaughter increased after weaning, and by 96 h levels of LH indicated a preovulatory surge was beginning. Follicular diameter increased with time after weaning, with increases in number of follicles >5 mm in diameter, and decreases in number of follicles <5 mm in diameter. Concentrations of LH, but not FSH, in AP were greater at both 60 and 96 h than at 0 h after weaning (P<0.01). Concentrations of GnRH in MBH and SME were greater at 60 and 96 h than at 0 h (P<0.05). The concentration of GnRH in HPA was increased only at 96 h after weaning. In both experiments, concentration of GnRH increased after weaning, concurrently with postweaning increases in serum FSH, serum and pituitary LH and follicular development. Thus we propose that initiation of estrus and ovulation after weaning may be associated with changes in production of GnRH.
Serum luteinizing hormone in prepuberal gilts after ovariectomy or adrenalectomy.
Serum luteinizing hormone (LH) concentrations after ovariectomy (OVX) and adrenalectomy (ADX) were studied in the prepuberal gilt. In Exp.I, gilts, 170 to 175 d of age and 80 to 85 kg body weight, were OVX (n = 5) or sham-OVX (n = 5). Blood samples were collected via jugular vein cannulae every 30 min for 8 h on d 1, 3, 5, 7 and 21 after surgery. In Exp. II, blood samples were collected via jugular vein cannulae every 30 min for 12 h on d 3, 5, 7 and 14 after surgery from five ADX, five sham-ADX and five nonsurgical control gilts of similar ages and weights as in Exp. I. In Exp. I, basal serum LH concentrations (means +/- SE, ng/ml) over all days were greater (P less than .05) in OVX (2.9 +/- .1) than in sham-OVX (1.1 +/- .2) gilts. Average basal serum LH concentrations were greater (P less than .05) on d 1 for both treatments than all other days sampled. The frequency of LH peaks (means +/- SE/8 h) was also greater (P less than .01) for OVX (3.5 +/- .3) than sham-OVX gilts (1.7 +/- .2). Similarly, the mean concentration of the LH peaks was greater (P less than .01) for OVX (4.1 +/- .2 ng/ml) than sham-OVX gilts (2.1 +/- .2 ng/ml). In Exp. II, mean basal serum LH concentrations, frequency of LH peaks and mean concentration of the LH peaks were similar for all treatments on each day sampled. The frequency of LH peaks (means +/- SE/12 h) was greater (P less than .05) on d 3 (3.4 +/- .3) than on d 5 (2.3 +/- .3) and d 7 (2.1 +/- .4), but similar to d 14 (2.8 +/- .5) in all treatments. In prepuberal gilts, ADX failed to influence serum LH concentration, whereas OVX caused a significant increase in serum LH concentration. We suggest that the ovary is the major steroid-secreting gland having a negative feedback on pituitary gonadotropin production in the prepuberal gilt.