Involvement of brain catecholamines in the gonadotropins-releasing mechanism(s) before puberty.

Abstract

The involvement of brain catecholamines (CA) in the neuroendocrine mechanism(s) that controls the secretion of pituitary gonadotropins has been clearly established in adult, but not in immature, rats. Daily administration of an inhibitor of CA synthesis, a-methyltyrosine (a- MT, ISO mg/kg ip) to 20-day-old hemiovariectomized (Hm Ovx) rats, completely suppressed the ovarian compensatory hypertrophy (OCH) present 4 days after operation. Combined treatment with β-MT and 1-3,4-dihydroxyphenylalanine (L-DOPA, 100 mg/kg ip), a precursor of brain noradrenaline (NA) and dopamine (DA), prevented the blocking effect of β-MT on OCH. The effect of a-MT was also abolished by DL-threo- 3,4-dihydroxyphenylserine (DOPS, 200 mg/kg ip), a drug which selectively restores brain NA levels. DL-p-Chlorophenylalanine (PCPA, 250 mg/kg ip), an inhibitor of serotonin (S-HT) synthesis, did not modify OCH. Pituitary FSH content was unaltered in hemiovariectomized rats treated with saline, β-MT or β-MT plus L-DOPA on comparison with values present in intact controls. Hypothalamic follicle stimulating hormone releasing factor (FSH-RF) disappeared completely in Hm Ovx controls; administration of β-MT to Hm Ovx rats resulted in the reappearance of FSH-RF in the hypothalamus, which was still present after combined treatment with β-MT plus L-DOPA. Biochemical determinations of NA, DA and S-HT provided evidence on the effects of the drugs used on actual brain monoamine levels. It is concluded that brain CA, namely NA, play a role in the regulation of FSH secretion before puberty; their underlying mechanism(s) of action is discussed. (Endocrinology90: 1267, 1972)