EFFECTS OF ADRENERGIC STIMULANTS ON THE SPLENIC DIAMETER, HEMOGLOBIN CONTENT AND HEMATOCRIT IN ANESTHETIZED DOGS - DETERMINATION OF THE ADRENOCEPTOR SUBTYPE RESPONSIBLE FOR CHANGES IN THE SPLENIC DIAMETER

Changes in splenic diameter measured by sonomicrometry in response to various adrenergic stimulants were estimated together with simultaneou sly measured arterial haemoglobin content (HGB) and haematocrit (HCT) in anaesthetized dogs. Splenic diameter decreased following intravenou s injections (i.v.) of adrenaline, noradrenaline and phenylephrine and splenic nerve stimulation associated with increases in arterial HGB a nd HCT, which were significantly attenuated by prazosin i.v. After pra zosin i.v., adrenaline i.v. increased splenic diameter significantly, but noradrenaline i.v. did not. Isoprenaline i.v. increased splenic di ameter transiently, followed by a decrease that was abolished by prazo sin i.v. During occlusion of splenic arteries and veins, adrenaline i. v. and phenylephrine i.v. did not cause any change in arterial HGB and HCT. Injection to splenic artery (i.a.) of phenylephrine induced a si gnificant decrease in splenic diameter that was attenuated by prazosin i.a. but not by yohimbine i.a. Clonidine i.a. did not change splenic diameter. The present results indicate that splenic contraction, which is mediated through alpha1-adrenoceptor activation, causes a signific ant increase in arterial HGB and HCT.