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The present study was conducted to investigate the influence of hemicastration and age at hemicastration on the subsequent testicular development of male rabbits through sexual maturity. Thirty New Zealand white rabbits were left intact or were hemicastrated on Day 35, 49, 77, or 105 postconception. Beginning at 7 mo of age, ejaculates were collected every other day for 1 mo, and the last ten ejaculates were used to quantify daily sperm output. At 8 mo, the rabbits were killed and their carcases, testes, testicular capsules, and epididymides were weighed. Testicular tissue was processed for quantification of sperm production rates by enumeration of homogenization-resistant spermatids and via histometric evaluation. Regardless of the age at hemicastration, this manipulation did not alter the development of the remaining testis as assessed from testis weight, numbers of Sertoli cells per testis, daily sperm production, or sperm output (p > 0.05). On the basis of these findings, it would appear that the development of the spermatogenic capacity of the remaining testis of the rabbit is not altered appreciably by hemicastration at a young age.

Germ cell degeneration during spermatocytogenesis and meiosis was investigated to explain the age-related decline in daily sperm production (DSP). Numbers of Types A-dark, A-pale, and B-spermatogonia, potential daily sperm production per g parenchyma (PDSP) based on type B-spermatogonia, early primary spermatocytes, and late primary spermatocytes, and DSP per g based on early spermatids were determined in 15 men aged 20 to 48 yr (mean +/- SEM, 33 +/- 2 yr) and 15 men aged 52 to 90 yr (65 +/- 3 yr). Testes obtained within 15 h of death (largely due to trauma or heart failure) were perfused vascularly with glutaraldehyde. The number of each cell type per g parenchyma was calculated as the product of the percentage of nuclei in the parenchyma times a correction factor for section thickness and nuclear diameter divided by the volume of a single nucleus of that cell type. Paired testicular weight was lower (p less than 0.01) in older men (33 +/- 3 g) than in the younger men (49 +/- 3 g). Younger and older men had similar numbers of A-dark, A-pale, and B-spermatogonia per g parenchyma. PDSP based on late primary spermatocytes and DSP based on early spermatids were lower (p less than 0.01) in older men than in younger men. In younger men, PDSP was similar (p greater than 0.05) between B-spermatogonia and late primary spermatocytes, whereas DSP measured at the spermatid level was abruptly lower than that estimated from younger cell types. Older men showed reduction in PDSP between early and late primary spermatocytes, with further reduction occurring in DSP at the spermatid level.(ABSTRACT TRUNCATED AT 250 WORDS)

At 1, 2, 4, and 7 weeks or 15 months postsurgery, bilateral denervation of the testes of mature male rats had no effect on basal levels of plasma testosterone, testicular weight, spermatogenesis, or mating behavior. However, bilateral denervation blocked an acute stress-induced rise of plasma testosterone. This is the first report of a possible role of testicular innervation in the mature male rat.

Two experiments established the relationships among total scrotal width (TSW), daily spermatozoal production (DSP), daily spermatozoal output (DSO) and extragonadal spermatozoal reserves (EGR) of dogs ejaculated daily. In Experiment 1, 11 dogs (14 to 36 kg) were ejaculated daily for two 10-day periods and in Experiment 2, seven dogs (15 to 47 kg) were ejaculated daily for two 20-day periods. Approximately six daily ejaculations were required for stabilizing DSO. After the second period of daily ejaculations, dogs were castrated or killed and the testes were weighed and DSP and EGR were determined. In Experiments 1 and 2, DSP averaged 11.7 +/- 0.5 and 16.7 +/- 1.4 X 10(6) per gram of testicular parenchyma, respectively, or 369 and 594 X 10(6) per dog. DSP per gram of testicular parenchyma was not significantly correlated with parenchymal weight for the same testis in either experiment (r = 0.04 and 0.26). Mean (+/- SEM) EGR of dogs in Experiment 1 were 4024 +/- 368 X 10(6) and 4791 +/- 767 X 10(6) in Experiment 2. Approximately 63% of the EGR were contained in the caput and corpus epididymidis, 36% in the cauda epididymidis and 1% in the ductus deferens. DSO averaged 79 and 82% of DSP for the 2 groups of dogs. Based on combined data for all 18 dogs, TSW was correlated with testicular weight (r = 0.95; P less than 0.01), DSP (r = 0.82; P less than 0.01) and DSO (r = 0.75; P less than 0.01). Thus, measurement of TSW is a useful predictor of a dog's ability to produce and ejaculate spermatozoa.

Administration of melatonin via subcutaneous Silastic capsules caused a marked reduction in testicular weight, and suppressed spermatogenesis in two species of photoperiodic rodents: golden hamsters and grasshopper mice. In marked contrast, melatonin failed to exert any demonstrable effect on testis weight or spermatogenesis in two species of nonphotoperiodic rodents: laboratory rats and house mice. These findingssuggest that melatonin, and by implication the pineal gland, may play a more importent role in regulating testicular function of rodents whose reproductive activity is markedly dependent upon seasonal changes in day length than of rodents whose reproductive performance is relatively insensitive to photoperiodic cues.