Changes in Leydig Cells and Luteinizing Hormone Receptors in Porcine Testis during Postnatal Development*

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Abstract
LH receptors have been characterized in porcine testis (Sus crofa L.) from birth to 220 days of age and have been related to interstitial tissue development (especially Leydig cells). The mean association constant (Ka) of ovine [3H]LH, was 7 ± 6 × 109 M-1 with no apparent age-dependent variation but with some significant individual variations. The concentration of specific LH receptor sites reached a maximum of 9 × 10-12 M/g testis between days 20–70, decreased to 3 × 10-12 M/g testis at the onset of puberty (up to 110 days), and remained stable at the same level in the adult. The total number of sites per testis essentially reflected the growth of the testis. Interstitial tissue occupied up to 80% of the volume of the whole testis during the first 30 neonatal days. It decreased to about 25% after 120 days. The Leydig cells in this tissue occupied the same proportion (70% of the volume of the whole testis) regardless of the age of the animals. The mean Leydig cell diameter reached a maximum of 20 μm at 30 days of neonatal life, decreased to a minimum of 10 μm at 90 days, and then increased to a stable value of 15 fim after puberty. The number of Leydig cells per unit volume varied with age, with a maximum of 3 × 108 cells/ml testis at 90 days, reaching a constant value of 6 × 107 cells/ml testis after puberty. These data suggest that each Leydig cell contains 80,000 specific LH-binding sites/cell 30 days after birth and 35,000 in the adult, with no observed periods without receptor sites. The number of receptors per cell is correlated to cell size rather than stage of sexual maturation.