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S Nelson

Publications and source records attributed to S Nelson.

At least 343 records · Page 19Linked to original sources
PubMed1981

The random transition model of the cell cycle. A critical review.

The random transition model of the cell cycle has received much attention in recent years in attempts to describe and explain variations in cell cycle times. In this review we suggest statistical procedures for fitting the model to experimental data in place of the invalid techniques currently used. However, we also argue that there have been misconceptions about criteria for quality of fit of the model, and consequent biological interpretations. Other models fit just as well, and the analyses we describe do not provide evidence for any particular biological mechanism.

Animals↗
PubMed1981

Synthesis and evaluation of novel alkylpiperazines as potential dopamine antagonists.

Several alkylpiperazines, monocyclic subfragments of known tricyclic neuroleptic agents, were evaluated as dopamine antagonists in the isolated rabbit ear artery preparation. Compound prepared and evaluated are of the general structure Ar-X-(CH2)n-Y, where X = C, O, and N, n = 1-3, and Y, for the most part, was 4-methylpiperazine. Those compounds where X - NH, n = 3, and X = (Z)-CH - CH, n = 2, with an electron-withdrawing group meta to the side chain, possess dopamine antagonist activity comparable to that of clozapine. It is concluded that the entire tricyclic structure of phenothiazine-like agents (or at least more than a monocyclic ring system) is necessary for optimal activity as a dopamine antagonist in the receptor preparation used in this study.

Animals↗
PubMed1981

Antihypertensive and hemodynamic actions of SCH 19927, the R,R-isomer and labetalol.

SCH 19927, one of the four chiral forms of labetalol, is approximately 4 times as potent as a beta adrenergic receptor blocker as the parent racemate, but is only one-third as potent in blocking alpha receptors. The present report describes its antihypertensive and hemodynamic actions. SCH 19927 and labetalol lowered blood pressure in hypertensive rats and dogs. SCH 19927 was somewhat more effective at lower doses, but the two agents produced comparable responses at higher doses. Both reduced blood pressure and peripheral resistance and increased cardiac output in anesthetized dogs. Intraarterial injection in to the femoral vascular bed, either in the presence or absence of neurogenic vasoconstrictor tone, resulted in dose-related vasodilatation. In contrast, alpha blockers, e.g., phentolamine and prazosin, are essentially devoid of vasodilator activity in denervated beds. It is concluded that vasodilatation is largely responsible for the antihypertensive response to labetalol and particularly to SCH 19927. SCH 19927 is a potentially useful agent which would be expected to reduce pressure in humans by two complementary mechanisms, beta blockade and vasodilatation. It should possess less orthostatic potential than labetalol.

Animals↗
PubMed1979

Mormon health.

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Demography↗
PubMed1977

LSD and d-amphetamine effects on fixed interval responding in the rat.

Food-deprived rats were trained to press a key which produced a food pellet for the first press after 3 min had elapsed (FI 3 min). Daily sessions consisted of 10 such intervals. Graded doses of LSD (0.04 - 1.28 mg/kg) and a d-amphetamine (0.5 - 2.0 mg/kg) were given 30 min before sessions. LSD produced a decrease in response rate at doses of 0.32 mg/kg and above, but did not disrupt the typical FI pattern of responding except at the highest dose (1.28 mg/kg). Amphetamine did not significantly alter the overall response rate, but caused a dose-related disruption of the FI response pattern, with previously low response rates increased more than higher rates, and occasional decreases in the previously highest rates. The experiment was repeated using the same rats responding on a multiple FIFR schedule. The presence of a 2000 Hz tone signalled FR periods; the tone was absent during FI periods. During the FR components, a pellet was produced after 30 responses had been emitted. The FI components were unchanged. LSD (0.08 - 0.32 mg/kg) again produced decreases in FI rate without altering the pattern, and amphetamine again altered the FI pattern without significantly changing overall rate.

Animals↗
PubMed1977

Relationship of microvascular disease in diabetes to metabolic control.

Dogs were made alloxan-diabetic and randomly distributed into either of two prospective treatment groups. In one group it was intended that the metabolic signs of diabetes be controlled poorly, and commercial insulin was administered in doses inadequate to prevent chronic, severe hyperglycemia and glucosuria. In the other group it was intended that the metabolic disorder be well controlled, and the animals received food and commercial insulin twice daily such that the hyperglycemia and glucosuria became mild or infrequent. Experimental improvement of the carbohydrate disorder was accompanied by amelioration of hyperlipemia and other clinical signs of deficient insulin activity. By 60 months of diabetes, retinal capillary aneurysms, pericyte ghosts, obliterated vessels, and other microvascular abnormalities typical of diabetes were apparent in each animal of the poor-control group. Better control was found to reduce significantly the incidence and severity of microvascular lesions. The data suggest that the mechanism responsible for diabetic retinopathy is initiated as a result of deficient insulin activity and that the development of the microvascular complications of diabetes are preventable and may be inhibited by careful control of the metabolic disorder.

Animals↗