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O. SCHIAFFINI
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P. SCACCHI
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The sequence of changes in gonadotrophin and/or sex hormone secretion observed during the sex cycle and the difference in the type of gonadotrophin control between male and female rats, can be related to changes in hypothalamic glucose oxidation (Scacchi, Moguilevsky & Schiaffini, 1973). This paper presents an attempt to determine whether a similar process to the one observed in the hypothalamus occurs in the limbic system, since this tissue is directly affected by gonadotrophin levels (Schiaffini & Martini, 1972).

The production of 14CO2 from [U-14C]glucose in the amygdala and hippocampus of albino rats was determined by the methods described in a previous paper (Scacchi et al. 1973). Cerebral cortex from the frontal region was used as control tissue. The following experimental groups were established: (a) female rats in dioestrus; (b) in pro-oestrus; (c) in oestrus; (d) ovariectomized and used 7 days after gonadectomy; (e) ovariectomized and

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J. A. MOGUILEVSKY
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P. SCACCHI
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It is generally accepted that the hypothalamus regulates gonadotrophin secretion by means of specific mediators synthesized in the hypothalamus (Martini, Fraschini & Motta, 1968) and usually called releasing factors. Considering that the gonadotrophin releasing factors are probably peptides (Schally, Arimura, Bowers, Kastin, Sawano & Redding, 1968) and that it is possible to demonstrate an alteration in the amount of these substances in the hypothalamus after gonadectomy (Piacsek & Meites, 1966; Watanabe & McCann, 1969), it was of interest to determine the RNA and protein content of the anterior, middle and posterior hypothalamus in normal and in castrated rats.

Male albino rats fed on the standard diet of the Instituto de Fisiología and weighing 150–180 g were used. Light and temperature were controlled (25 °C, 12 h light and 12 h darkness). Food and water were available ad libitum. Gonadectomy was performed 6 weeks before the animals were decapitated and the

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J. A. MOGUILEVSKY
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P. SCACCHI
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L. RUBINSTEIN
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Department of Neuroendocrinology, Centro de Investigaciones Médicas Albert Einstein (CIMAE), Luis Viale 2831, Buenos Aires, Argentina and *Department of Obstetrics and Gynecology, UCLA School of Medicine, Los Angeles, California, U.S.A.

(Received 18 January 1977)

It is generally accepted that the administration of androgens to female rats in the neonatal period suppresses cyclic gonadotrophin release and a tonic gonadotrophin release occurs (Barraclough, 1966; Gorski, 1971). The tonic or male gonadotrophin pattern characteristically shows higher levels of plasma and pituitary follicle-stimulating hormone (FSH) and serum prolactin compared with female rats (Johnson, 1967, 1971; Kragt & Ganong, 1968; Neill, 1972).

In spite of the fact that the neonatal administration of androgens also induces changes in the reproductive physiology of adult male rats (Johnson & Witscht, 1963; Johnson, Yasuda & Sridharan, 1964; Morrison & Johnson, 1966), the effect of androgenization on gonadotrophin secretion in this sex is not clear.

The purpose of the present study

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D. P. CARDINALI
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MARÍA R. FAIGÓN
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P. SCACCHI
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J. MOGUILEVSKY
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SUMMARY

The effects of melatonin on serum prolactin levels were examined in ovariectomized rats primed with oestradiol and progesterone, and subjected to bilateral superior cervical ganglionectomy or pinealectomy.

Ganglionectomy resulted in a significant depression of the serum prolactin concentration, as well as in impairment of the prolactin release evoked by administration of steroid. Treatment with melatonin increased serum prolactin in control but not in ganglionectomized rats. Injection of melatonin potentiated the steroid-induced release of prolactin in control rats; this effect of melatonin was not detected in ganglionectomized rats. Pinealectomy did not affect basal prolactin levels, nor impair the release of prolactin evoked by steroid treatment; however, it was effective in blocking the melatonin-induced release of prolactin in vehicletreated rats, as well as the potentiation of steroid-induced prolactin release by melatonin. Intracranial surgery by itself increased prolactin release. These results suggest that systemically administered melatonin needs an intact pineal gland to augment serum prolactin levels.

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