Tissue-specific activity of pentose cycle oxidative enzymes during feeder lamb development

Relationships between pentose cycle oxidative activity and differential fat growth were evaluated. Rambouillet wether lambs (n = 60) were slaughtered serially at 0, 40, 80, and 120 d on feed (15 lambs/group). Rack dissection and kidney fat weights were collected, and longissimus muscle i.m. fat content was determined. Postmortem longissimus muscle, s.c. fat, intermuscular fat (INT), and kidney fat (KP) samples were assayed in vitro for glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activity (nanomoles.minute-1.gram of tissue-1), and samples were subjected to electrophoresis (PAGE) to separate tissue-specific isoforms. Allometric coefficients for rack components indicated that s.c. fat was the earliest-maturing, slowest-growing depot, INT was the latest-maturing, fastest-growing depot, and i.m. fat was intermediate (P < .05). Kidney fat grew faster than carcass weight and, as carcass weight increased, the growth rate of KP accelerated (P < .05). Enzyme activities increased until 40 d on feed and declined thereafter. Activities differed across tissues and time on feed end points (P < .05). Ratios of G6PDH:6PGDH, reflecting flux through the oxidative phase of the pentose cycle and, therefore, lipogenic activity, suggested growth patterns similar to those indicated by allometric analysis, except in the i.m. fat depot. Development of i.m. fat initially was intermediate to KP and INT, but G6PDH:6PGDH ratios increased with time on feed, suggesting a different regulatory mechanism and maturing pattern. Multiple forms of G6PDH were detected with PAGE, and although polymorphism was not detected, a tissue-specific isoform was isolated for INT fat.