Control of gonadotropin secretion in the ovine fetus. II. A sex difference in pulsatile luteinizing hormone secretion after castration.

Gonadal involvement in the control of fetal LH secretion was examined by studying LH pulsatility in 12 chronically catheterized male (9 castrate and 3 sham-control) and 12 female (8 castrate and 4 sham-control) ovine fetuses operated upon in utero at 106-116 days gestation (term = 147 days). Fetuses were studied longitudinally over a 2- to 30-day period in castrates and over a 2- to 37-day period in controls. LH pulsatility was determined from blood samples obtained every 15 min over a standard 3-h observation period and assayed for LH by RIA (NIH LH S16 standard). In female fetuses there was no significant difference in LH pulse frequency between castrates (25 pulses in 32 periods; 1 pulse/3.8 h of observation) compared to controls (15 pulses in 15 periods; 1 pulse/3.0 h). LH pulse frequency was similar in the sham-castrate males (11 pulses in 17 periods; 1 pulse/4.6 h). In contrast, LH pulse frequency was significantly higher in the castrate male group (90 pulses in 42 periods; 1 pulse/1.4 h) compared to that in each of the other 3 groups (P less than 0.005). LH pulse frequency did not vary with gestational age in castrate and control females or in control males. In castrate males, however, LH pulse frequency declined significantly (P less than 0.005) with advancing gestation from 80 pulses in 32 periods (1 pulse/1.2 h) before 130 days compared to 10 pulses in 10 periods (1 pulse/3.0 h) after 130 days. Thus, LH pulse frequency was indistinguishable in castrate vs. eugonadal males after 130 days. The absence of a castration effect on LH pulsatility in male fetuses older than 130 days was confirmed in an additional group of 8 male fetuses (5 castrate and 3 sham-controls) operated upon at 121-130 days gestation and studied over a 2- to 20-day period. Overall, LH pulse amplitude was similar in male [4.7 +/- 0.5 ng/ml (+/- SE)] and female (3.9 +/- 0.5 ng/ml) fetuses and did not vary as a function of gonadal status or gestational age. The postcastration increment in LH pulse frequency in the castrate male fetus from 108-130 days gestation delineates a role of the fetal testis in feedback regulation of LH secretion at this stage of development. The absence of a postcastration rise in LH pulse frequency in the castrate female indicates that the fetal ovary does not play a similar role.(ABSTRACT TRUNCATED AT 400 WORDS)