Unmated male rats were raised in social isolation and grouped, and mated males were raised in cohabitation with hysterotomized females. The unmated males were raised under conditions providing different intensities of female odours.
In isolation, the penis muscles, levator ani, penis and the seminal vesicle tissue of the males exhibited a relative atrophy similar in degree to that prevalent in grouped males. Isolated males grew faster and had larger ratios of kidney to body weight and adrenal to body weight than grouped males. A correlation between these two ratios was observed.
Continuous exposure to female odours, from weaning to 136 or 240 days of age, did not affect the general atrophy of the accessory reproductive organs either in isolated or in grouped, unmated males.
Grouping and exposure to female odours reduced the amount of secretion contained in the seminal vesicles and the size of the bulbourethral glands.
It was concluded that social conditions, i.e. isolation and grouping, and continuous exposure to female odours, have only minor effects on the reproductive system of unmated males; conversely, under conditions of cohabitation, heterosexual mating is the factor responsible for preventing the atrophy of the reproductive system in males.