Inter- and intra-fat pad variation in vascularization and the release of 14C-labelled fatty acids in mice.

Adult laca mice were dosed orally with 150 microliters whole milk containing 2.5 microCi of either labelled stearic acid ([1-14C]18:0; n 20) or labelled linoleic acid ([1-14C]18:2; n 20). The mice were killed in groups of four at 6, 12, 24, 48 and 96 h following dosing and samples of perirenal and epididymal fat pads were taken from both inner and outer sites at each location. Significant differences in the rate of loss of label between sites were found. No differences (P = 0.018) between fat pad locations (epididymal v. perirenal) were found. A significant interaction between rate of loss of labelled fatty acid and site (P = 0.019) reflected the fact that between-site variations in this context were confined to labelled linoleic acid. In a second study weanling adult (n 10) and adult (n 10) mice were killed and their epididymal and perirenal fat pads prepared for histological examination. Both transverse and longitudinal sections were taken at the inner and outer sites of each fat pad location. Following staining, both the size and number of blood vessels were measured using computer-linked microscopy. In all instances there were significant differences between sites with the inner site consistently showing greater numbers and areas of blood vessels. In general the number of blood vessels in the inner site tended to be greater in older mice, while the reverse was seen for younger mice. The results lend support to the concept of multiple pools of triacylglycerol-fatty acids in adipose tissue such that the main determinant of short-term supply of essential fatty acids is the quantity recently ingested.