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

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 approximately 20 litres/nmol; FSH approximately 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.(ABSTRACT TRUNCATED AT 250 WORDS)