Sex Differences and Hormonal Control of Testosterone Metabolism in Rat Pituitary and Brain

Abstract

The in-vitro conversion of testosterone to 17\g=b\-hydroxy-5\g=a\-androstan-3\x=req-\ one (5\g=a\-dihydrotestosterone, DHT) and 3\ g=a\ , 17\g=b\-dihydroxy-5\g=a\-androstane (3\g=a\-androstanediol, DIOL) in pituitary and slices of brain regions was compared between male and female rats. Intact pituitaries from male rats formed 2\m=.\5times more DHT and 1\m=.\5times more DIOL than those of females. A small sex difference was also detected in the hypothalamus, males again being higher than females. No sex differences could be detected in other brain regions. However, DHT formation in the brain was regionally differentiated with higher conversion rates in hypothalamus than in cortex, hippocampus, amygdala, pineal gland or cerebellum. The highest transformation, however, was found in the mid-brain. Metabolism in the pre-optic area was as low as that in the cortex. 5\g=a\-Dihydrotestosterone and DIOL formation in the pituitary increased several-fold after gonadectomy in both sexes and the sex difference disappeared. Little or no increase occurred after thyroidectomy or adrenalectomy. The increase in pituitary DHT formation after gonadectomy could be attenuated or prevented both by treatment with testosterone propionate and with oestradiol benzoate. Replacement therapy, particularly with oestradiol benzoate, gave rise to a sex difference reminiscent of that of normal animals. No significant change in pituitary DHT formation occurred in adult females which had been treated with testosterone propionate on the 4th day of life.The results suggested a close relationship between DHT formation and activity of gonadotrophin secretion, particularly at the level of the pituitary.

Androgen Metabolism in the Brain of the Green Anole Lizard (Anolis carolinensis): Effects of Sex and Season

“…Similarly, in the Wilson's phalarope, 5␣-reductase is greater in the anterior hypothalamus/preoptic area of breeding than of nonbreeding males (Schlinger et al, 1989). However, the enzyme activity is generally similar between the sexes and seasons (Denef et al, 1973;Schumacher and Balthazart, 1986;Schlinger and Callard, 1987;Silverin and Deviche, 1991). The different patterns in the regulation of aromatase and 5␣-reductase are mainly due to T sensitivity.…”

“…Similar effects on 5␣-reductase have been detected in a few cases. For example, male-biased sex differences in the enzyme's activity are present in the hypothalamus and/or preoptic area of the rat (Denef et al, 1973), little brown bat (Callard et al, 1983), and Japanese quail (Schumacher and Balthazart, 1986). Similarly, in the Wilson's phalarope, 5␣-reductase is greater in the anterior hypothalamus/preoptic area of breeding than of nonbreeding males (Schlinger et al, 1989).…”

“…and myelin from the optic and sciatic (reviewed in Melcangi et al, 2000) nerves. Thus, the high levels of 5␣-reductase activity in the brainstem of anoles and other vertebrate species (Denef et al, 1973;Callard et al, 1978a,b) might be due to myelinated motor tracts in this part of the brain. However, the cellular localization of 5␣-reductase in the green anole has yet to be determined.…”

Characterization and measurement of dehydroepiandrosterone sulfate in rat brain.

“…Several steroid metabolism enzymes have been described in brain, in particular hydroxysteroid dehydrogenases (27)(28)(29), steroid-5a-reductase (30)(31)(32), aromatase (33), and steroid hydroxylases (28,34,35). Steroid sulfokinase activity has been demonstrated in monkey and human brain (28) and steroid sulfatase has been found in rat (36) and human (37) …”

Effects of Testosterone Metabolites and Estrogen in the Midbrain Control of Courtship Behavior in the Male Ring Dove (<i>Streptopelia risoria</i>)

“…Hormone diffusions from the implant did not appear to be responsible for these re sults since many implants within 1 mm of the ICo region failed to activate nest-cooing. These data support the idea that the midbrain along with the hypothalamic region mediate male courtship behavior.In mammals, such as rats, testosterone (T) is metabo lized in significant quantities to 5a-dihydrotestosterone (5a-DHT) via a 5rx-reduction pathway and converted to es tradiol-1711 (E) via an aromatase route [50], The rat brain is capable of these metabolic conversions and it shows region al differences in the type and quantity of hormone transfor mations [22,33, 40, 41]. Furthermore, T action, as well as a combined effect of peripheral DHT action and central E ac tion, stimulate copulatory behavior in male rats [systemic studies: 11,24,32,45; intracranial studies: 14,19,31,44].…”