Selective regional vasoconstriction underlying pressor effects of galanin in anaesthetized possums compared with cats

1. Intravenous administration of porcine galanin (5 nmol kg-1) caused a rise in mean blood pressure in the brush-tailed possum, Trichosurus vulpecula, from 58 +/- 1.6 to 106 +/- 1.6 mmHg. This effect is in contrast to the cat, in which no significant change in blood pressure was recorded in response to galanin (88 +/- 2.3 vs. 86 +/- 2.4 mmHg). 2. Cardiac output and regional blood flow distribution were assessed by distribution of radioactive microspheres in four anaesthetized possums and four cats, before and after administration of galanin. 3. Cardiac output was 289.8 +/- 14.0 ml min-1 in the cat and 189.9 +/- 25.5 ml min-1 in the possum. Galanin administration did not significantly change cardiac output in either species. 4. In the possum, galanin administration caused large increases in resistance to flow in the spleen, gut, adrenal glands, kidney, skin and carcass. The largest increase was in the kidneys, where renal blood flow fell to 6% of control levels. 5. In the cat, changes in resistance were small. Small increases in resistance to flow in muscle and carcass were offset by small decreases in resistance in the lungs and kidneys. 6. The results suggest that the pressor effect of galanin in the possum is the result of direct vasoconstrictor action in several vascular beds, in contrast to the cat, in which such effects are few and weak.