Testicular atrophy (TA) and decreased plasma luteinizing hormone (LH) levels were observed in the adult male rat after treatment with 500 µg of estradiol benzoate (EB) on the first day of life, while administration of 1 mg of testosterone propionate (TP) on the same day was also associated with TA but increased LH levels. TA and no changes in plasma LH levels were seen when the treatment was performed with similar doses of both steroids on day 5 of life. In no case were plasma follicle-stimulating hormone (FSH) levels altered by these treatments. No differences in basal LH and FSH levels were found in adult females after treatment with 100 µg of EB or 1 mg of TP on day 5. LH response to castration was lower in neonatally androgenized and estrogenized adult male and female rats than in their respective controls, while FSH response was scarcely modified. In conclusion, neonatal treatment with EB or TP in both sexes induced alterations in LH control mechanisms without changing those of FSH.

No abstract

The present study was designed to determine whether the modification of exposure time to large doses of estrogens provided a reliable model for early changes in reproductive aging. Silastic implants containing estradiol benzoate (EB) in solution were placed into 5-day-old female Wistar rats and removed 1 day (Ei1 group) or 5 days (Ei5) later. In addition, 100 micrograms [corrected] EB dissolved in 100 microliters corn oil was administered s.c. to another group (EI). Control rats received either vehicle implants or 100 microliters corn oil. Premature occurrence of vaginal opening was observed in all three estrogenized groups independently of EB exposure. However, females bearing implants for 24 h had first estrus at the same age as their controls and cycled regularly, and neither histological nor gonadal alterations could be observed at 75 days. Interestingly, they failed to cycle regularly at 5 mo whereas controls continued to cycle. On the other hand, the increase of EB exposure (Ei5, EI) resulted in a gradual and significant delay in the onset of first estrus and in a high number of estrous phases, as frequently observed during reproductive decline. At 75 days, the ovaries of these last two groups showed a reduced number of corpora lutea and an increased number of large follicles. According to this histological pattern, ovarian weight and progesterone (P) content gradually decreased whereas both groups showed higher estradiol (E2) content than controls. This resulted in a higher E2:P ratio, comparable to that observed in normal aging rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgenized, oestrogenized and control female and male rats were used to establish possible differences in the alteration of the prolactin control system. Neonatal treatment involved administration of oestradiol benzoate or testosterone propionate (TP) on days 1 and 5 to the males and on day 5 to the females. Oil-treated animals were used as controls. Plasma prolactin levels were measured in these animals during adulthood (a) before gonadectomy, performed on day 80, and 27 days after gonadectomy and (b) on the 2 days (at 10.00 and 17.00 h) after administration of a single dose of TP to gonadectomized animals. Oestrogenized rats had the highest plasma prolactin concentrations just before and after gonadectomy. Testosterone propionate increased plasma prolactin levels in all groups. This response was more notable in the female than in the male groups, and was highest in the oestrogenized animals. Temporal rhythms of the prolactin response to TP were daily, perhaps circadian, with increased levels in the afternoon compared with those in the morning. This pattern was not present in oestrogenized females and androgenized males. Results suggest (a) that oestrogens and androgens given neonatally differ in their ability to alter the prolactin control system, and (b) that females seem to be more sensitive than males to changes in hypothalamic differentiation induced by neonatal steroid treatment.

Female rats were submitted to light-darkness, to constant light on day 60 or to constant light from birth. Plasma prolactin was measured on days 80,100 and 120 in all experimental situations before ovariectomy was performed. 10 days later, a blood sample was taken and the animals were injected subcutaneously with 75 µg of estradiol benzoate. Blood was again drawn on 2 consecutive days. Results showed that: (a) prolactin levels were higher in the groups submitted to prolonged periods of constant light (60–120 days); (b) after ovariectomy prolactin levels decrease but remain higher in these same groups, and (c) constant light produced a higher prolactin response to estradiol benzoate. These data indicate that the length of exposure to constant light may be a critical factor in the development of alterations in the control of prolactin secretion.