DEVELOPMENTAL-CHANGES OF TESTICULAR GONADOTROPIN RECEPTORS AND SERUM GONADOTROPIN-LEVELS IN 2 STRAINS OF MICE

The relationship between testicular gonadotropin receptors and serum g onadotropin concentrations during sexual maturation was studied in two inbred mouse strains ( BALB/cAJcl and ICR/Jcl strains). The specific binding of [I-125]iodo-FSH per unit testicular weight was the highest at 21 days of age in the BALB/cAJcl strain and 7 days in the ICR/Jcl s train, followed by a rapid decrease thereafter. The total FSH binding in the ICR/Jcl strain was significantly decreased at 35 days from the level at 28 days and remained low thereafter. However, such decrease w as not observed in the BALB/cAJcl strain. Scatchard plot analyses show ed that the changes in FSH binding were due to the changes in the numb er of binding sites and not in the affinity of binding. The specific b inding of [I-125]iodo-LH per unit testicular weight reached a peak aro und puberty , and the total LH binding tended to remain constant after puberty in both strains. During early testicular developmental stages , the increase in the serum FSH levels was well correlated with the nu mber of FSH receptors. Prepubertal increase in LH binding sites occurr ed after the rise in the serum FSH levels. To conclude, we found a str ain difference in the regulation of the number of FSH receptors, indic ating that down-regulation is not unique to the C57BL/6NCrj strain, bu t that it is not universal among strains of mice.