Male Sprague–Dawley rats were used in two experiments in which a procarbazine bolus (400 mg kg⁻¹ body mass) was administered with or without testicular circulatory isolation in the form of brief clamping of the spermatic cord and gubernaculum during drug administration. Separate tests of aggressiveness, sexual motivation, copulatory performance and paternity over the subsequent 6 weeks were used to assess functional changes resulting from testicular circulatory isolation. Experiment 1 compared intermale aggression and sexual motivation of animals in groups receiving procarbazine plus testicular circulatory isolation lasting 0, 15 or 45 min with that of animals in control groups with no clamp and no drug. Experiment 2 used a 2 × 2 factorial design to evaluate sexual performance and resulting paternity in animals 2 months after testicular circulatory isolation and drug exposure compared with that in control animals. Procarbazine treatment induced minimal disruption of normal interest in a receptive female, copulatory measures (intromissions or ejaculations) and structural integrity of seminal vesicles, bulbospongiosus muscles and ventral prostate glands. Animals exposed to the drug without testicular circulatory isolation were significantly less aggressive than animals in other groups. The most profound influence of procarbazine was on paternity. Males exposed to procarbazine with or without testicular circulatory isolation impregnated notably fewer females than did control males that were not exposed to the drug. There was no evidence of recovery of normal fertility up to 10 weeks after exposure to the drug. In conclusion, the deleterious influence of procarbazine on androgen-sensitive processes appears to be specific to intermale aggression and to fertility. The testicular circulatory isolation technique, for 45 min in particular, softened the impact of the drug on social behaviour, although procarbazine suppressed fecundity even with testicular circulatory isolation.

The number of Sertoli cells is important in spermatogenesis as noted by significant correlations between the number of Sertoli cells and the number of germ cells observed as early as type B₂ spermatogonia in the horse. However, the stage within spermatocytogenesis at which these relationships first occur is unclear. The relationships between the number of Sertoli cells and parenchymal weight and the number of germ cells during the mitosis of spermatogenesis were determined in 184 adult horses to identify the developmental stage (that is, the earliest germ cell) at which significant relationships are established. The total numbers of all types of A spermatogonia and of specific subtypes (A₁, A₂, A₃, B₁ or B₂) of spermatogonia were correlated with the number of Sertoli cells and with parenchymal weight. The number of each cell type was calculated using stereology. The number of Sertoli cells was correlated (P < 0.01) with parenchymal weight (r = 0.85) and with daily sperm production (r = 0.83), and parenchymal weight was correlated (P < 0.01) with daily sperm production (r = 0.89). The number of Sertoli cells was correlated (P < 0.01) with the number of type A (r = 0.81) and A₁ (r = 0.74) spermatogonia. Parenchymal weight was correlated with the number of type A (r = 0.80) spermatogonia and with the number of A₁ (r = 0.67) spermatogonia. These data are consistent with the hypotheses that the number of Sertoli cells is important in determining testicular size and daily sperm production and that the relationship of daily sperm production to the number of Sertoli cells or to parenchymal weight has already been established at the level of primitive spermatogonia.