Developmental changes in gonadotrophins and testicular gonadotrophin receptors in the pig, from neonatal to adult life

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Abstract
Changes in the concentrations of LH and FSH testicular receptors have been studied in the pig, from neonatal to adult life, and correlated with blood LH, FSH and testosterone concentrations. Quantification of gonadotrophin receptors was performed in equilibrium binding studies, using homologous systems. The presence of high-affinity binding sites for LH and FSH (association constant (Ka): LH ∼ 20 litres/nmol; FSH ∼ 10 litres/nmol) was demonstrated in the testes of all animals studied. The apparent affinity of LH and FSH receptors did not change significantly with age. During the first weeks of life, there was a transient rise in LH receptor content, reaching a maximum of 8·7 ± 2·2 (mean ± s.e.m.) pmol/g testis at 24 days of age. This was correlated with a peak in testosterone secretion and reflects the second wave of interstitial cell proliferation in the pig. A second increase in the number of LH receptors occurred after 12 weeks of age and corresponds to pubertal maturation and final differentiation of adult Leydig cells. During this period, circulating concentrations of testosterone markedly increased without any significant variation in LH blood levels, suggesting a change in testicular sensitivity to LH in the maturing pig. A continuous increase in FSH receptor content was observed from the neonatal to the adult pig. This increase occurred in two phases. During the first 2 months of life, the increase in the number of FSH receptors exceeded that of testis growth rate and resulted in an increase in FSH receptor concentrations which reached a peak at 12·1 ± 1·8 pmol/g testis, at week 9. After this time the increase in the amount of FSH receptors was slower than that of testis weight gain, leading to a decrease in receptor concentration. Since changes in the amounts of LH and FSH receptor concentrations were not correlated with variations in gonadotrophin concentrations in the blood, an inductive role for FSH on LH receptors, as has been shown in the rat, could thus not be demonstrated in the pig. J. Endocr. (1986) 111, 301–308

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