Altered catecholamine contents in vascular and nonvascular tissues in genetically hypertensive rats.

We have measured the catecholamine (CA) contents in hearts, mesenteric vasculature, abdominal aorta, inferior vena cava, vasa deferentia and salivary glands from genetically hypertensive rats (SHR) and normotensive Kyoto-Wistar rats (WKY). We noted differences between the norepinephrine (NE) contents of individual tissues from SHR and WKY rats and have used two different analytical procedures for the measurement of NE to confirm these differences. Comparisons between tissue contents of NE in SHR and WKY rats indicated a greater content of NE in the following tissues from the SHR: heart, mesenteric artery, abdominal aorta, inferior vena cava and vasa deferentia. A modest elevation of NE [but not epinephrine (E)] was observed in adrenal glands from SHR rats. The NE contents of salivary glands from SHR and WKY rats were indistinguishable from each other. The results suggest that there may exist a generalized increase in NE contents in the peripheral vasculature of SHR rats. Furthermore, this increase is also present in the vasa deferentia, but not the salivary gland. The results draw attention to altered concentrations of NE in vascular and selected nonvascular tissues in the SHR.

Effect of age on substance P levels in the rat mesenteric artery and vein.

The content of substance P in the vasculature of Fischer 344 rats 6 to 27 months of age was determined by radioimmunoassay. Substance P could not be measured in the subclavian vein, femoral artery and vein or cerebral arteries of 6 month old rats. Levels of substance P in the mesenteric artery and vein of 6 month old rats averaged 4.8 +/- 1.0 and 8.3 +/- 1.8 pmole/g wet weight (n = 6-7), respectively. At 20 months of age, substance P levels in the vein were significantly increased. At 27 months, levels of substance P in both mesenteric artery and vein were increased to almost twice the values found in younger animals. This increased substance P content could reflect increased nerve density, or, more likely, an increased substance P content in each nerve ending. In the latter case, it is not possible to distinguish between increased content due to decreased nerve activity or increased content which would result in increased amounts of substance P released with each nerve impulse.

Catecholamines in the vasculature of the rat and rabbit: dopamine, norepinephrine, epinephrine.

A highly sensitive radioenzymatic assay for the measurement of catecholamines in small blood vessels was applied to the measurement of the levels of norepinephrine (NE), dopamine (DA) and epinephrine (E). The results showed the presence of NE, E and DA in all segments of rat or rabbit vascular tissue analyzed. The predominant catecholamine in the vasculature from both species was NE, and the contents of E and DA were similar for most vessels. Unexpectedly large concentrations of E were associated with rabbit blood vessels.

Resistance of noradrenaline in blood vessels to depletion by 6-hydroxydopamine or immunosympathectomy.

1. The degree of the decrease in the noradrenaline concentrations caused by 6-hydroxydopamine or immunosympathectomy was different in different areas of the cardiovascular system.2. In rats or guinea-pigs 6-hydroxydopamine depleted the noradrenaline content of the heart by 90%, of the mesenteric vein by 80% and of the mesenteric artery and aorta by 30-60%. Immunosympathectomy elicited a 70% reduction in the cardiac noradrenaline but only a 50% reduction in the noradrenaline of the blood vessels of the rat.3. The tyrosine hydroxylase activity of the heart, blood vessels, or adrenal glands was not significantly altered 2 weeks after 6-hydroxydopamine. Nor was the monoamine oxidase activity in heart or blood vessels changed.4. The inconsistent ability of both 6-hydroxydopamine and immunosympathectomy to abolish experimental hypertension may be due to the partial persistence of noradrenaline and functional sympathetic nervous system activity in the blood vessels.