The mean level of plasma testosterone was 2 ng/ml in neonates and 0.4 ng/ml in infants ; it increased to 3 ng/ml during onset of meiosis and reached 10 ng/ml in adults. The profile of testosterone was positively and significantly correlated with the total volume and total number of Leydig cells (P <0.01 and P < 0.02, respectively) and with changes in their cytoplasmic volume (P < 0.0011. Moreover, plasma testosterone levels were positively and significantly correlated with changes in Leydig cell SER content i.e. SER volume density and mean absolute volume per cell (P < 0.001), total SER in the whole testis (P < 0.011. ).Introduction.

Plasma testosterone, 5\g=a\-dihydrotestosterone(DHT), \g=D\4-androstenedione, dehydroepiandrosterone (DHA) and oestradiol-17\g=b\concentrations of crab-eating macaques after birth were analysed by RIA. The profiles of plasma testosterone and DHT exhibited four phases: (1) a neonatal phase (0 to 3\p=n-\4months of age) with considerable synthetic testicular activity; (2) a phase of 'infancy' (generally up to 29 months of age) during which the values of both androgens were low; (3) a prepubertal phase (generally up to 43 months of age) when circulating values oscillated with wider individual variations, and (4) a pubertal phase when the concentrations increased in parallel and concomittantly with the onset of meiosis and the establishment of spermatogenesis. The testosterone values continued to increase, reaching adult values at about 5\p=n-\6 years of age, whereas DHT levels tended to stabilize from 4\p=n-\5 years. Relatively high androstenedione values during the neonatal phase decreased progressively until puberty, then increased again slowly up to the adult stage when they plateaued at about neonatal levels. The DHA levels were high during the first months, decreased at about 1 year, remained stable during infancy and prepuberty and then declined again during puberty. At about 5 years, the values were 28% of those in neonates. There was no evidence of an adrenarche before the first signs of sexual maturity were observed. Oestradiol-17\g=b\concentrations were high at birth and until 3 months, then decreased and remained steady from 1 year of age until adulthood, except at the onset of puberty (27\p=n-\30 months of age) when high values were again noted. Our results show that, during the neonatal period, the testis exhibited considerable secretory activity.

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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 X 10(9) 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 X 10(-12) M/g testis between days 20-70, decreased to 3 X 10(-12) M/g testis at the onset of puberty (up to 100 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 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 micrometer at 30 days of neonatal life, decreased to a minimum of 10 micrometer at 90 days, and then increased to a stable value of 15 micrometer after puberty. The number of Leydig cells per unit volume varied with age, with a maximum of 3 X 10(8) cells/ml testis at 90 days, reaching a constant value of 6 X 10(7) 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. (Endocrinology 108: 625, 1981)

The effect of weight of fatty tissue on fat and plasma androstenone and on plasma testosterone relationships in the young boar was studied. For this purpose, hCG stimulation of steroid testicular production was performed in 12 boars and fat androstenone concentration subsequently measured. In addition plasma androstenone and testosterone were determined in 8 of them, previously cannulated. The results show that: 1) although plasma testosterone response to hCG stimulation was similar in all boars, fat and plasma androstenone responses were very variable between boars, 2) weight of fatty tissue appeared to have little influence, if any, on androstenone exchanges between plasma and fatty tissue and 3) plasma androstenone/testosterone ratio appeared to be less variable within boars than between boars.The data show that there is probably some between\x=req-\ boars-variability in the respective rates of elimination of testosterone and androstenone.