Ontogeny of gonadal luteinizing hormone and follicle-stimulating hormone receptors in the fetal pig and related changes in gonadotropin and testosterone secretion.

Fetuses of Large White and Meishan sows were collected at 28, 35, 49, 56, 75, 90, 103, and 113 days of gestation. LH, FSH, and testosterone concentrations were measured either in amniotic fluid (Days 28-56) or in arterial umbilical blood (Days 75-113). Gonads were analyzed for their content of LH and FSH receptors and RNA transcripts. Most of these parameters were similar in the two breeds, except that the mean testosterone concentration was higher (p < 0.05) in the plasma of 75-113-day Meishan fetuses (309 and 136 pg/ml in males and females, respectively) than in Large White fetuses (152 and 109 pg/ml). Higher testosterone concentrations were detected in males than in females, either in amniotic fluid (114 vs. 81 pg/ml, p < 0.05) or in plasma (230 vs. 122 pg/ml, p < 0.01). In contrast, higher gonadotropin concentrations were found in the plasma of females than in that of males (2 vs. 1.6 ng/ml LH and 4.2 vs. 1.4 ng/ml FSH, p < 0.05). In the testis, 2-3 pmol/g gonad of LH and FSH receptors were detected as early as Day 28. This value increased to 10-13 pmol/g between 35 and 56 days before declining to 3-5 pmol/g after Day 90. In ovaries, LH receptors were detected in the earlier period (Days 28-56) at 1-3 pmol/g before diminishing to 0.1-0.4 pmol/g. FSH receptors were higher at Day 28 (1 pmol/g) than at any subsequent stage (0.1-0.4 pmol/g). The gonadal content of RNA transcripts was significantly higher in testes than in ovaries.(ABSTRACT TRUNCATED AT 250 WORDS)