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SUMMARY
Two days after a single or repeated administration of p-chlorophenylalanine (p-CPA; 316 mg/kg i.p.) in the rat, a marked diminution to 20% of control levels of brain 5-hydroxytryptamine, partial but not complete abolition of the circadian pituitary—adrenal rhythm and a profound decrease in adrenal responsiveness to ether stress or exogenous adrenocorticotrophin were found. Pituitary—adrenal activity in unstressed or stimulated animals was assessed by the level of corticosterone in plasma and the corticosteroid production by adrenal tissue in vitro. The effect of p-CPA administration on changes in pituitary—adrenal periodicity were concomitant with a reduction in food intake and body growth and a pronounced increase in adrenal weight. In the light of the marked functional alterations after p-CPA treatment, the proposed relationship between decreased brain 5-hydroxytryptamine content and pituitary—adrenal periodicity is questioned.
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SUMMARY
A simple and rapid assay for the quantitative determination of melanocyte-stimulating hormone (MSH) activity, using skin fragments of the lizard Anolis carolinensis in vitro, is described in detail. This assay, in which a quantal response (e.g. induction of a brownishgreen colour) can be detected by visual observation, allows determination of MSH activity in up to 50 samples/day by one person, using the skin of one lizard. The mean dose found to induce this colour change was 0·15 ng synthetic α-MSH/ml (range 0·02–0·5 ng/ml). The assay shows high accuracy, reproducibility and specificity. Anterior and posterior lobe hormones as well as pituitary catecholamines do not interfere with the determination of pituitary MSH activity.
The method is compared with the assay using hypophysectomized frogs (Rana pipiens) in vivo. Determinations of MSH in pituitary extracts by both methods gave quantitatively similar results when determined with α-MSH as the reference substance. However, when β-seryl MSH was used as a reference, the two assays gave different results for the MSH activity of the pituitary extracts. This indicates that MSH from the rat pituitary gland has a biological activity similar to that of α-MSH rather than to that of β-seryl MSH.
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SUMMARY
Injection of 250 μg 6-hydroxydopamine (6-OHDA) into the lateral ventricle of adult male and female rats resulted 1 week later in: (1) a lowered brain content of noradrenaline to 20% and dopamine to 40–50% that of control levels but no change in brain serotonin content; (2) a slight reduction in male and no change in female body weight; (3) no change in adrenal weight; (4) minor or no changes in diurnal pituitary–adrenal periodicity or in the responsiveness of this system to ether stress, laparotomy or exposure to a strange environment and handling. Dexamethasone blockade of the diurnal rise in adrenocortical activity was also unchanged.
Intracerebral administration of 200 μg 6-OHDA to newborn male and female rats in three sequential doses of 40, 60 and 100 μg, resulted at 12 weeks of age in (1) a lowered brain content of noradrenaline and dopamine to 10% that of control levels but no change in brain serotonin; (2) a 30% decrease in body weight; (3) no change in adrenal weight; (4) minor or no changes in pituitary–adrenal periodicity nor in the responsiveness to ether stress and exposure to a strange environment and handling.
When minor changes after 6-OHDA treatment of adult or neonatal rats were found, they always pointed to a stimulatory function of brain catecholamines in pituitary–adrenal activity. It is concluded however that a severe and chronic depletion of brain catecholaminergic systems has no important consequences for the normal functioning of the pituitary–adrenal system.
