Influence of Age on the Response to Paranatal Administration of a Low Dose of Androgen

A single injection of testosterone propionate (TP, 10 μg) was given subcutaneously to female rats of 1, 2, 3, 4, 5, 6, 8 and 10 days of age. The females were laparotomized during their early postpubertal days and again as young adults, and the presence or absence of ovarian corpora lutea recorded. The effect of postnatal administration of TP varied with the age at injection and at observation. Ten μg TP can be given through day 4 to prevent even the initial pubertal ovulation, and through day 6 to prevent ovulation after a postpubertal delay during which ovulation does occur. This influence of animal age and the delay in the appearance of the anovulatory syndrome suggest that the concept of a critical period during which hypothalamic neurones are competent to respond to TP lacks specific and clear definition. (Endocrinology82: 1001, 1968)