Morphological & morphometric studies on liver in rats subjected to repetitive heat stress.

Morphological and morphometric studies were conducted under light microscope on paraffin sections (H&E) of liver from controls and experimental rats subjected to repeated heat stress for 4 h/day, at 38 degrees +/- 0.5 degree C (relative humidity 65-82%) for 2-8 consecutive days. The morphometric variables were derived by intersection-point counting method, using simple square lattice test system A100. Twinning of liver cell plates and anisocytosis characterised morphological changes in rats exposed to heat twice. Following five heat exposures, rat liver showed ballooning degeneration of hepatocytes, associated with sinusoidal compression and loss of normal liver cell plate pattern. The degenerative changes in liver parenchyma were more pronounced in rats that underwent eight heat exposures. Despite hepatocytic degeneration, the numerical density of hepatocytes (Nvh) and the volume density of hepatocytes (Vvh) increased with the increase in number of heat exposures, indicating associated heat induced acceleration in hepatocytic proliferation. A successive fall, with increase in the number of heat exposures, in the sinusoidal length density (Jvs) and in the numerical density of Kupffer cells on area (Nak) revealed progressive damage to hepatic-vascular endothelium, which suggest an adverse effect on the immune status of the animals.