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Biomedical subjects

D N Harris

Publications and source records attributed to D N Harris.

At least 73 records · Page 4Linked to original sources
PubMed1979

Effects of chronic treatment with captopril (SQ 14,225), an orally active inhibitor of angiotensin I-converting enzyme, in spontaneously hypertensive rats.

The effects of hydralazine (3 mg/kg) and the angiotensin I-converting enzyme (ACE) inhibitor captopril (SQ 14,225) (100 mg/kg) on mean arterial blood pressure, plasma renin activity, urinary volume and urinary Na+,K+, and aldosterone concentrations were examined in spontaneously hypertensive rats of the Okamoto and Aoki strain (SHR) after oral daily dosing for 2 weeks, 3 or 6 months. Captopril caused progressive cumulative reductions in blood pressure resulting in normalization of pressure after 6 months of dosing. Hydralazine also significantly reduced blood pressure but not to the level of normotensive rats of the Wistar-Kyoto strain (WKY). Reductions in heart size paralleled the changes in blood pressure, normalization of cardiac hypertrophy occurring after captopril but not hydralazine. Plasma renin activity increased approximately 2-3 fold after hydralazine and 15-fold after captopril. Neither hydralazine nor captopril had any consistent effects on 24-hr urine volume, urinary Na+,K+ or aldosterone excretion. These results indicate that chronic inhibition of ACE with captopril induces normalization of blood pressure in SHR, a normal-renin model of hypertension.

Aldosterone↗
PubMed1979

Inhibition of adenylate cyclase in human blood platelets by 9-substituted adenine derivatives.

A series of 9-substituted adenine derivatives inhibited adenylate cyclase activity (ATP pyrophosphate-lyase (cyclizing) EC 4.6.1.1) of a particulate preparation of human blood platelets. A 3--6 fold elevation of adenylate cyclase activity by prostaglandin E1 (PGE1) was inhibited in a concentration-related manner by 9-(tetrahydro-5-methyl-2-furyl) adenine (SQ 22,538), 9-(tetrahydro-2-furyl) adenine (SQ 22,536), 9-cyclopentyladenine (SQ 22,534), 9-furfuryladenine (sQ 4647) and 9-benzyladenine (SQ 218611). The I50 values ranged from 21 microM for SQ 22,538 to 140 microM for SQ 21,611. These same adenine derivatives reversed the inhibition by PGE1 of ADP-induced aggregation and the PGE1-stimulated elevation of adenosine 3':5'-monophosphate (cyclic AMP). The reversal of platelet aggregation inhibition by SQ 22,536 and SQ 4647 was concentration-related with I50 values of 30 microM in each case, whereas SQ 22,534 and SQ 21,611 reversed inhibition by 30% at 100 microM. SQ 22,536, SQ 22,534 and SQ 21,611 also blocked the increase in cyclic AMP levels in a concentration-related manner with I50 values of 1, 4 and 60 microM, respectively. SQ 4647 inhibited the elevation of cyclic AMP by more than 85% at 1000 microM. The adenine derivatives had no effect on platelet aggregation or on cyclic AMP levels in the absence of PGE1. These results provide additional evidence that the inhibition of platelet aggregation by PGE1 is mediated by cyclic AMP.

Adenine↗
PubMed1978

Effects of SQ 14,225, an orally active inhibitor of angiotensin-converting enzyme on blood pressure, heart rate and plasma renin activity of conscious normotensive dogs.

Oral administration of SQ 14,225 (0.03--3 mg/kg) to conscious normotensive dogs caused inhibition of the pressor response to intravenously administered angiotensin I (AI), the duration of which was dose-dependent. All doses of 0.1 mg/kg or greater caused 85--95% inhibition 30 min after administration whereas 0.03 mg/kg produced only a 25% inhibition. Pressor responses to angiotensin II (AII) were not similarly inhibited. Blood pressure was moderately reduced in a dose-related manner and followed the same pattern as inhibition of the AI pressor responses. The maximum change occurred after 1.0 mg/kg with only a more rapid onset occurring after the 3.0 mg/kg dose. Heart rate was not appreciably changed. SQ 14,225 also increased plasma renin activity (PRA), the levels and duration of which were dose-related. These data indicate that SQ 14,225 is an orally effective, potent inhibitor of angiotensin I-converting enzyme (ACE) in dogs. It appears that in mongrel dogs, ACE inhibition results in a slight to moderate reduction in blood pressure and an increase in PRA.

Angiotensin I↗
PubMed1978

Chronic antihypertensive effects of captopril (SQ 14,225), an orally active angiotensin I-converting enzyme inhibitor, in conscious 2-kidney renal hypertensive rats.

Indirect systolic blood pressure (SBP) was monitored in 9 groups of 15 male conscious 2-kidney renal hypertensive rats (RHR) for over 6 months. Daily oral dosing with captopril (SQ 14,225, D-3-mercapto-2-methylpropanoyl-L-proline, 30 mg/kg), an orally active angiotensin I-converting enzyme inhibitor, lowered SBP 30--50 MM Hg during this period. Withdrawal of captopril for 5 days at 1, 3 and 6 months resulted in gradual return of SBP to control levels without overshoot. Resumption of dosage with captopril again decreased SBP. Daily oral dosing with hydrochlorothiazide (HCTZ, 6 mg/kg/day) alone for 6 months had little or no effect on SBP, but increased the antihypertensive effect of captopril. Daily oral dosing with hydralazine (6 mg/kg) caused an initial marked antihypertensive effect greater than that of captopril but almost complete tolerance developed within 4 weeks of dosing. Highest survival rates occurred in RHR treated with captopril plus HCTZ. In four other similarly treated groups of RHR and normotensive rats (NR), least cardiac hypertrophy and highest plasma renin activity occurred in captopril-treated animals compared with vehicle-treated controls. Plasma renin activity was about 2 to 4 fold higher in the rats dosed with captopril compared with vehicle-treated rats. Heart weight/body weight ratios, initially higher in the two RHR groups compared to NR, decreased only in the captopril treated group to or near those of the NR groups. These results indicate that chronic treatment with captopril decreased SBP and cardiac weights of RHR, and that HCTZ, or possibly other diuretics, can augment the antihypertensive effect of captopril while having little or no effect by themselves.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1978

Hypotension induced by inhibition of angiotensin-converting enzyme in pentobarbital-anesthetized dogs.

The mechanism of the hypotensive response produced by inhibition of the angiotensin converting enzyme was studied in pentobarbital anesthetized dogs. A recently developed potent inhibitor of the converting enzyme, SQ 14,225 (D-3-mercapto-2-methyl propanoyl-L-proline), administered i.v. to intact dogs resulted in a rapid marked decrease in blood pressure. In nephrectomized dogs, SQ 14,225 retained significant hypotensive activity, although the absolute magnitude of the decreases in blood pressure were less than had been observed in dogs with intact kidneys. SQ 14,225 also lowered blood pressure when administered to intact dogs in which angiotensin II receptors had been blocked with the receptor antagonist Sar1,Ala8-angiotensin II. This apparent ability of SQ 14,225 to decrease blood pressure in the absence of a functional renin angiotensin system was shared by a structurally dissimilar, nonapeptide, angiotensin converting enzyme inhibitor, SQ 20,881 (Glu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro). SQ 20,881 also produced significant decreases in blood pressure in nephrectomized dogs. These findings indicate that the angiotensin converting enzyme inhibitors, SQ 14,225 and SQ 20,881 may lower blood pressure in anesthetized normotensive dogs via a mechanism unrelated to either the renin angiotensin system or the renal kinin system.

Anesthesia↗
PubMed1975

Modulators of cyclic AMP systems.

On the basis of the data reported here, one may conclude that although many agents that act in the central nervous system are modulators of the action of cyclic AMP, it is difficult to establish a direct connection between the pharmacologic activity and the levels of cyclic AMP in the brain. This lack of interrelation applies to the benzodiazepines as well as to the pyrazolopyridines. The data for members of the latter group are somewhat frustrating in this regard, since an excellent correlation has been shown to exist between the potency of inhibition of PDE and activity in the antianxiety test. In measurements of steroidogenesis in the isolated adrenal cell, the correlation between activity in vito and the conflict assay is even better. The data presented here and reported elsewhere (Shimizu et al., 1974; Kelly et al., 1974; Mayer and King, 1974; King and Mayer, 1974) provide evidence that agents that act as inhibitors of PDE in cell-free systems exert their influence on cyclic AMP in tissue slices of the brain of guinea pigs by mechanisms that seem not to be related to an effect on PDE. Papaverine, and possibly chlordiazepoxide, may act by releasing agonists that, in turn, stimulate the accumulation of cyclic AMP. This activity is blocked bo other inhibitors of PDE, such as theophyline. Results obtained by the use of platelets are refreshingly clear. Inhibition of aggregation has been shown to occur when the level of cyclic AMP is raised, and a suggestive exists that the most potent inhibitors of platelet PDE are the best potentiators of the action of PGE1 in blocking aggregation. The study utilizing drugs collected from a large number of therapeutic classes makes clear that it is difficult to attribute the mechanism of action for any of the classes studied to modulation of cyclic AMP. An unexpected finding of this study, however, was the fact that pharmacologic agents include an unusually large number of inhibitors of PDE as compared with agents chosen at random. This finding provides a powerful tool for the biochemical pharmacologist who is examining large numbers of compounds in the search for potential drugs.

Adenylyl Cyclase Inhibitors↗