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E Vijayan

Publications and source records attributed to E Vijayan.

At least 55 records · Page 3Linked to original sources
PubMed1981

Neurotensin and substance P: differential effects on plasma cholesterol levels in conscious ovariectomized rats.

Circulating plasma cholesterol levels were measured in conscious ovariectomized rats, bearing an indwelling silastic catheter in the external jugular vein, after intravenous (i.v.) pulse injection of 100 microliter 0.9% NaCl containing varying doses of neurotensin and/or substance P. Control injections of saline or decapeptide LH-RH or phosphate buffer did not modify plasma cholesterol levels. 10 or 20 micrograms doses of neurotensin produced a significant and dose-related increase in plasma cholesterol levels while similar doses of substance P had an opposite effect and induced a significant decline in plasma cholesterol levels in ovariectomized rats. 4-APP, a drug which selectively inhibits hepatic secretion of lipoproteins, significantly lowers plasma cholesterol to levels comparable to those produced by substance P. 4-APP and substance P induced hypocholesterolemia was readily reversed by a single dose of neurotensin. These findings indicate that neurotensin acts to increase circulating cholesterol levels and substance P antagonizes this hypercholesterolemic effect of neurotensin presumably by acting at some step in cholesterol transport. Reversal of the inhibitory effects of 4-APP and substance P on blood cholesterol by neurotensin may be through its action on hepatic secretion of lipoproteins, since 4-APP is known to lower circulating cholesterol by its specific action on hepatic secretion of lipoproteins.

Adenine↗
PubMed1978

The effect of systemic administration of dopamine and apomorphine on Plasma LH and prolactin concentrations in conscious rats.

The effect of systemic administration of various doses of dopamine (DA) and apomorphine (APM) on plasma gonadotropin and prolactin (Prl) concentrations in ovariectomized (OVX) as well as in ovariectomized, estrogen-progesterone (OEP)-primed rats bearing indwelling jugular venous catheters was evaluated. Intravenous (i.v.) infusion or pulse injection of 0.9% NaCl had no significant effect on plasma titers of LH or Prl. I.v. infusion of DA at 4 micrograms/kg-b.w./min induced a progressive increase in circulating LH concentration in OEP rats while infusion at a similar dose in OVX animals had no effect on plasma LH. I.v. injection of 100 micrograms DA or APM significantly increased LH at 15 min in OVX rats. Similarly, in OEP rats 100 micrograms of DA elevated plasma LH at 30 and 90 min while APM induced a significant elevation of plasma LH at 15 min after injection. In OVX rats injection of DA i.p. at a dose of 5 mg/kg-b.w. did not alter plasma LH levels, but a dose of 50 mg/kg-b.w. produced a significant reduction in plasma LH concentration. APM injected i.p. at either 5 or 50 mg/kg-b.w. doses was nearly equally effective in lowering plasma LH and the suppressive effect was significantly greater than with similar doses of DA. A single injection of LH-RH (100 ng in 0.2 ml of 0.9% NaCl) in animals pretreated 15 min earlier with an effective dose of APM (5 mg/kg-b.w.) produced a peak increase in LH titers 15 min after injection. The increment in plasma LH following LH-RH in APM-treated rats was comparable to that in rats which had received saline instead of APM. Prl levels were significantly lowered by each dose of DA and APM in OVX as well as in OEP rats. There was no significant change in plasma FSH titers induced by either drug in any of the experiments. It is concluded that DA may have different actions depending upon the dose and the endocrine state of the animal. Thus, i.v. infusion of low doses of DA in OEP animals or by pulse injection in both OVX and OEP rats can elevate plasma LH by activating the release of LH-RH from the hypothalamus, while large doses of DA in OVX animals may suppress the release of LH-RH.

Animals↗
PubMed1978

Catecholaminergic regulation of TSH and growth hormone release in ovariectomized and ovariectomized, steroid-primed rats.

Third ventricular injection of dopamine (DA), Piribedil (ET-495), a DA receptor stimulator, norepinephrine (NE), epinephrine (E) and systemic administration of larger doses of DA and the receptor stimulant, apomorphine (APM), were used to evaluate their role in the regulation of TSH and GH secretion in ovariectomized (OVX) as well as ovariectomized, estrogen-progesterone treated (OEP) rats. Intraventricular or i.p. injection of DA or its agonists, ET-495, and APM, caused a lowering of plasma TSH and an elevation of plasma GH concentration in OVX as well as in OEP rats. In contrast, intraventricular injection of NE or E increased plasma TSH and GH concentration. On the basis of these results it is concluded that the central dopaminergic system is inhibitory to TSH secretion, as reflected in our exeriments by the significant reduction of TSH levels. On the other hand, the noradrenergic and adrenergic system has a stimulatory role on the release of TRH as evidenced by the increase in plasma TSH levels. Activation of dopaminergic, noradrenergic and adrenergic systems appears to promote release by hypothalamic GH releasing hormone as reflected in the enhanced concentration of plasma GH, but the precise physiological role of these biogenic amines in modulating the release of TSH and GH hormone remains to be elucidated.

Animals↗