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Biomedical subjects

H J Granger

Publications and source records attributed to H J Granger.

At least 91 records · Page 5Linked to original sources
PubMed1982

Autoregulation of blood flow within individual arterioles in the rat cremaster muscle.

Autoregulatory responses to alterations in arterial or venous perfusion pressure were determined for individual arterioles within the rat cremaster muscle. The cremaster muscle of pentobarbital anesthetized rats (50 mg/kg, ip) was surgically exposed and maintained in a controlled tissue bath for visualization by in vitro television microscopy. Cremaster bath PO2 was controlled at either a high (approximately 70 mm Hg) or low (approximately 19 mm Hg) level. Inside diameter and red blood cell velocity were measured for individual first (1A), second (2A), or third (3A) branching order arterioles, and instantaneous blood flows within each arteriole were calculated. To measure the autoregulatory responses, we decreased arterial perfusion pressure to the microvascular bed by gradually occluding the sacral aorta. Significant autoregulation was observed in all orders of vessels, but, in general, autoregulation was more pronounced at all vessel levels when bath PO2 was low, and the autoregulatory gain was greater for the smaller vessels compared to the larger vessels. Elevation of venous pressure within the vascular bed by gradual occlusion of the inferior vena cava led to a significant vasoconstriction of the smaller vessels, suggesting that a significant myogenic component was present. The vasoconstriction response to elevated venous pressure was more pronounced when bath PO2 was high. Our data are not consistent with a purely myogenic or purely metabolic mechanism, but suggest that both mechanisms are simultaneously contributing to the local vascular regulation.

Animals↗
PubMed1982

Proximal-tubule-like epithelium in Bowman's capsule in spontaneously hypertensive rats. Changes with age.

Kidneys were samples from male spontaneously hypertensive rats (SHR) and normotensive rats (WKY) in four groups. Renal tissues were examined in 64 rats: 6 SHR and 6 WKY rats 8 and 16 weeks of age and 10 SHR and 10 WKY rats 32 and 64 weeks of age. Tissue samples were fixed, processed, and stained by routine histologic procedures. The parietal layer of Bowman's capsule in 100-115 renal corpuscles from right to left kidney sections was classified as squamous or cuboidal epithelium. The cuboidal epithelium was similar in structure to that of the proximal tubule. Quantitative information from right and left kidneys was pooled, because the data did not differ significantly. The percentages of renal corpuscles with proximal tubule-like epithelium present at the parietal layer of Bowman's capsule in the SHR was 13%, 35%, 44%, and 81% at 8, 16, 32, and 64 weeks, respectively. In WKY rats the values were 4%, 0.5%, 5%, and 13% at 8, 16, 32, and 64 weeks, respectively. The increase in the percentage of renal corpuscles with proximal tubule-like epithelium in SHR Bowman's capsules suggest an association between this tissue and hypertension. The modified layer of Bowman's capsule may be a response to an increase in blood pressure, may have some role in the etiology of hypertension, or may be irrelevant to hypertension.

Aging↗
PubMed1979

Autoregulation of superior mesenteric flow in fasted and fed dogs.

Pressure-flow relations in the intestinal vasculature were obtained by producing stepwise reductions of intestinal perfusion pressure with an adjustable metal clamp placed upon the descending thoracic aorta. To eliminate intervention of the baroreceptor reflex, systemic arterial pressure was maintained constant by a pressure compensation system connected to the two carotid arteries. In the fed dogs, autoregulatory vasodilatory responses to reduced perfusion pressure maintained flow within 5% of control in the 85-125 mmHg range. In 30% of the fed dogs, superior mesenteric flow actually increased as perfusion pressure was reduced in the pressure range 85-125 mmHg, indicating superregulation of flow in the intestinal vasculature. The degree of flow autoregulation in the fasted dog was less than in the fed dog. Moreover, superregulation of intestinal flow was not observed in any of the fasted animals. These data suggest an intimate link between parenchymal activity and local flow control in the small intestine.

Animals↗
PubMed1979

Regulation of cardiac output during rapid volume loading.

Interactions between heart rate (HR) and the Frank-Starling mechanism in augmenting cardiac output (CO) during acute volume loading were studied in dogs under varying conditions. In normal conscious dogs with low HRs of 70--90 beats/min, end-diastolic diameter (EDD) was maximal and CO was increased reflexly by cardioacceleration. By contrast, anesthetized open-chest dogs with high HRs ranging from 140 to 160 beats/min, responded with bradycardia and CO was adjusted solely by increasing stroke volume (SV). In anesthetized open-chest dogs with low HRs, EDD was less than maximal and increases in both HR and SV contributed to augment CO. These data show that both the cardioacceleration reflex and the Frank-Starling mechanism are important determinants of the cardiac response to elevated preload. Although the relative contribution of each control mechanism varies with initial conditions, their interplay extends the range of cardioregulation beyond that attainable by either loop operating alone.

Animals↗
PubMed1978

Effect of changing metabolic rate on local blood flow control in the canine hindlimb.

This study examined the effect of changing hindlimb metabolic rate on hindlimb blood flow control in anesthetized dogs. The hyperemias induced by graded levels of arterial hypoxia and the degree of steady state autoregulation evoked by changes in blood pressure were measured. Metabolic rate was increased above the resting value by direct electrical stimulation of hindlimb muscles at rates from 0.5 to 1.5 pulses/second, and in three dogs was reduced by cooling. In response to 6 minutes of arterial hypoxia, hindlimb blood flow steadily increased. At rest, and at each level of muscle stimulation, the steepness of the response increased as arterial oxygen saturation (SAO2) decreased. At all levels of SAO2, the response was steeper at increasing stimulation rates. For SAO2 greater than 50%, the relationship between the percentage increase in blood flow from control and SAO2, however, was unaffected by the degree of muscle activity, suggesting that during mild to moderate hypoxia the dynamics of the response were similar whether the muscles were at rest or exercising. The responses to severe hypoxia (SAO2 less than 50%) during stimulation were significantly enhanced compared with those at rest. Autoregulation of blood flow was measured in the steady state by comparing the relative change in blood flow from control with the relative change in blood pressure that produced it. Steady state autoregulation was weak at rest, but improved markedly with increasing muscle stimulation. Conversely, cooling the hindlimb depressed the resting steady state autoregulation. A close correlation was found between the degree of autoregulation and the hindlimb metabolic rate. The results suggest that tissue metabolic rate determines the precision of local blood flow control.

Animals↗