Changes with Age in Levels of Serum Gonadotropins, Prolactin, and Gonadal Steroids in Prepubertal Male and Female Rats

Abstract

Radioimmunological determination of serum LH, FSH, and estradiol concentrations in prepubertal female rats demonstrates the temporal coincidence of increased serum levels of these hormones between days 9 and 21. Serum FSH and estradiol levels are continuously high during that time, whereas interindividual fluctuations in LH levels were enormous. No high LH, FSH, and estradiol levels were observed between day 21 and puberty, during which time serum prolactin and progesterone gradually increased. Serum testosterone in the female immature rats stayed uniformly low. It is suggested that increased serum estradiol levels in the presence of low prolactin levels (between day 10 and 20) act in a positive feedback fashion on the CNS-pituitary axis. The resulting increased gonadotropin levels are later (between day 20 and puberty) decreased by an inhibitory action of prolactin and/or progesterone on pituitary gonadotropin release. In male rats serum FSH and prolactin, which were low during the first 3 weeks, increased later to reach high levels during puberty. Serum LH was slightly elevated during the 2nd and 3rd week of life at which time serum progesterone also increased to reach the highest levels in the prepubertal period. Serum testosterone was higher in male than in female rats for the first 3 weeks of life; the difference between both sexes was significant but not striking. Between day 21 and the prepubertal period the testosterone levels were relatively low, but they increased again during puberty. Sex differences in androgen levels (measured with a less specific antibody) were more pronounced whereas estradiol levels in males showed the same pattern between birth and puberty as in the female littermates. These results suggest that not only testosterone but also other, not yet identified, androgens may be involved in the masculinzation of the brain.

Regulation of the hepatic synthesis of α2u globulin and its corresponding messenger RNA in maturing male rats

“…The levels of serum testosterone showed a slow rise from 48-66 days of age, which was followed by a sharp rise after 66 days of age. A biphasic rise in the level of serum testosterone in the maturing male rat has also been reported by Dohler and Wuttke [29]. Unlike the biphasic rise of serum testosterone the daily urinary output of cllzu globulin and hepatic levels of the mRNA for ozu globulin showed an almost linear rise from 48-70 days of age.…”

Developmental estrogen exposures predispose to prostate carcinogenesis with aging☆

“…Similar to androgens, circulating levels of estradiol are high during the fetal and early neonatal life in both humans and rodent models (24) and there is compelling evidence that the developing prostate gland is particularly sensitive to these estrogens. During the third trimester of in utero development in humans, rising maternal estradiol levels and declining fetal androgen production result in an increased estrogen/testosterone (E/T) ratio.…”

Ontogeny of fear-, anxiety- and depression-related behavior across adolescence in C57BL/6J mice

“…Depression-related behavior was also tested using a pharmacologically-validated test, the forced swim test [11]. The subjects employed for this study were C57BL/6J mice, aged four, six or eight weeks considered to approximate to human early adolescence, peri-adolescence and early adulthood, respectively [12,30,45]. The C57BL/6J inbred strain was chosen on the basis of its widespread use in behavioral neuroscience research and its inclusion as a 'group A' priority strain in the Mouse Phenome Project; an international effort to provide the biomedical research community with phenotypic data on the most commonly used mouse strains (http://aretha.jax.org/pubcgi/phenome/mpdcgi?rtn=docs/home).…”