The ontogeny of immunoreactive beta-endorphin in fetal, neonatal, and pubertal testes from mouse and hamster

Derivatives of proopiomelanocortin (POMC), physicochemically similar to beta-endorphin and desacetyl alpha MSH, have been identified in adult testes, where these peptides were localized to Leydig cells. In the present study, the presence of immunostainable derivatives of POMC was established in fetal, neonatal, and pubertal testes with the unlabeled antibody peroxidase-antiperoxidase method. Specificity of staining was established by absorption of primary antisera with excess antigen. In the mouse, immunoreactive beta-endorphin was detectable in a few primitive interstitial cells on day 14 of gestation, the day after testicular differentiation. Thereafter, the number of immunostainable cells progressively increased throughout fetal life, so that at birth, they comprised 55% of the total interstitial cells. After birth, the number of immunostaining cells declined, so that they were only 12% of interstitial cells by 5 days of age. After 10 days of age, the number of immunopositive cells progressively increased, and by 40 days, interstitial cells showed intense staining comparable to that in adult mice. At 10 days of age, when the number of immunostainable cells was low, hCG treatment increased both the number and staining intensity of beta-endorphin-positive cells to those seen in adult testes. Antibodies directed against gamma MSH, a peptide within the N-terminal segment of POMC, also produced specific staining of fetal and adult interstitial cells in the mouse. In the hamster, the pattern of staining with anti-beta-endorphin in fetal, neonatal, and pubertal interstitial cells was similar to that observed in mice; the number and staining intensity of immunostainable cells increased during fetal life, declined after birth, and rose again at puberty.

1) the number and staining intensity of immunostainable interstitial cells have two peaks in mouse and hamster, at birth and after puberty; 2) the number and staining intensity of mouse interstitial cells can be increased by hCG; and 3) the development of immunostainable beta-endorphin activity correlates with the previously reported spontaneous and hCG-induced maturation of morphology and enzyme activities of Leydig cells.