MEASUREMENT OF BLOOD FLOW AND LIPOLYSIS IN THE HINDQUARTER TISSUES OF THE FAT-TAILED SHEEP IN VIVO

¹ Dairy Research Unit, Department of Animal Husbandry, University of Sydney, Camden, New South Wales, Australia
² Rumen Biochemistry, Animal and Dairy Science Research Institute, Irene, South Africa

Karakul and Namaqua-Afrikander sheep, both of which are fat-tailed breeds, were examined for suitability as models for studying lipid metabolism in vivo. The anatomy of the blood supply to the hindquarters of both breeds was examined, and a technique developed for sampling the venous outflow from the fat tail. The composition of the tail and the rest of the hindquarters was determined and found to be similar in both breeds. The hindquarters contained 35% fat, about half of which was located in the tail (72-74% fat). Rates of blood flow through the whole hindquarters, tail adipose tissue and leg muscle of Karakul ewes were measured. Tritiated water (TOH) was used for measurement of specific blood flow and p-aminohippuric acid (PAH) for measurement of absolute blood flow. The specific blood flow rate for tail adipose tissue was 3·62 ± 0·12 ml.min^-1.100 g^-1 and absolute blood flow was estimated as 74 ± 7 ml.min^-1. The absolute flow through the rest of the adipose tissue in the hindquarters was similar to that flowing through the tail, and together they represented about 15% of the total absolute flow through the whole hindquarters, 794 ± 131 ml.min^-1 measured directly using PAH. Total blood flow through the hindquarters estimated from the specific flow rate (using TOH) and the mass of the hindquarters was 761 ± 50 ml.min^-1. The absolute blood flow through the hindquarters of Namaqua-Afrikander ewes (626 ± 39 ml.min^-1) was lower than that measured in the Karakul ewes, but the difference was not significant (P 0·10). The rates of net release from tail adipose tissue of Karakul ewes measured in vivo were 3·0 ± 0·6 and 2·0 ± 0·2 µmol.min^-1. 100 g^-1 for free fatty acids and glycerol respectively. Intravenous infusion of noradrenaline (2µg.min^-1.kg^-1 liveweight) increased venoarterial differences of both free fatty acids and glycerol 2- to 3-fold and blood flow increased by about 60%. As a result, in response to noradrenaline, net releases for both free fatty acids and glycerol increased 4-fold.