Differentiation of blood vessels in the adipose tissue of lean and obese fetal pigs, studied by differential enzyme histochemistry.

Abstract

Subcutaneous adipose tissue was obtained from fetuses removed from pregnant obese (Ossabaw) and lean (crossbred) sows at three stages of gestation (70, 90, and 110 days). Histochemical analysis for nucleo-side phosphatase (NPase), alkaline phosphatase (APase), and NADH tetrazoleum reductase (NADH-TR) was conducted on fresh-frozen cryostat sections. Age- associated changes in NPase and NADH-TR reactions in the arteriolar system were correlated with the morphological development of the medial layer of arterioles and arteries. For instance, a strong NPase reaction in small arterioles was associated temporally with the assumption of a normal smooth muscle cell morphology and arrangement in the medial layer. In the youngest fetuses, strong NADH-TR reactions were only evident in small and presumptive arterioles and venules (associated with fat cells). Little NADH-TR reactivity was evident in larger arterioles and venules in 70-day tissue. Arteries and large arterioles were distinguished from veins and venules (strong reactions vs. weak reactions) with NADH-TR and NPase reactions in the oldest fetuses. In the younger fetuses, the NPase distinction (arterioles vs. veinules) was obvious before NADH-TR distinction. Small adipocyte-associated vessels were APase positive in the youngest fetuses, but APase reactivity was limited to short segments of vessel between arterioles and capillaries in the oldest fetuses. With the following exceptions, all the above observations were independent of fetal strain. In obese fetuses (110 day) small venules and small arterioles were equally reactive for NPase activity. Capillaries in obese fetuses (110 day) were NADH-TR reactive, whereas no activity was evident in capillaries from lean fetuses (110 day).(ABSTRACT TRUNCATED AT 250 WORDS)