SEPARATE ROLES OF ANDROGEN AND ESTROGEN IN THE MANIPULATION OF GROWTH AND EFFICIENCY OF FOOD UTILIZATION IN FEMALE RATS

The roles of androgen and oestrogen in the perinatal and postpubertal stages of development on the masculinization of female patterns of growth have been investigated in several experiments in rats. A stimulatory effect of testosterone on subsequent growth and efficiency of food utilization was only observed when administered perinatally to intact females as the propionate ester. Thus females which were untreated (or androgenized) perinatally and ovariectomized at weaning failed to grow more rapidly or utilize food more efficiently when treated with mixed testosterone esters from 36 to 38 days of age. Also autoimmunity to luteinizing hormone releasing hormone (LH-RH) had little effect on the growth or efficiency of food utilization of male rats, although testicular development was grossly affected. An inhibitory effect of oestrogen on subsequent growth and efficiency of food utilization was demonstrated by surgical ovariectomy and by autoimmunity to LH-RH. Also perinatal administration of oestradiol benzoate to intact female rats depressed growth below that of untreated intact litter-mate females until about 50 days of age. Then oestradiol benzoate-treated female rats grew to a larger size than untreated intact litter-mates but not to a heavier weight than untreated litter-mate females which like the oestradiol benzoate-treated females, were ovariectomized at 18-21 days of age. Both of these groups of female rats differed markedly in weight gain from females which were perinatally androgenized and ovariectomized at weaning. The effects of androgenization and ovariectomy on weight gain were comparable and additive in female rats fed restrictedly or ad libitum. Nevertheless, androgenized+ovariectomized female rats fed restrictedly or ad libitum failed to grow as rapidly as male rats. Some additional factor(s) prevents complete masculinization of the female pattern of development. The stimulatory effects of androgenization and ovariectomy on the growth of females appear to be related to endocrine mechanisms controlling the onset of pubertal changes in somatic development.