Hypophysectomy and adrenalectomy decrease Ca2+-induced swelling of rat liver mitochondria.

Hypophysectomized rats showed significant modifications in Ca2+-induced swelling and MgATP-induced contraction of liver mitochondria. Two-three months after operation, maximal swelling (MS), rate of swelling (VS), maximal contraction (MC) and rate of contraction (VC) were decreased by 77 (MS), 83 (VS), 79 (MC) and 62 (VC) % (in all cases P less than 0.05 as compared with normal rat mitochondria). Treatment of hypophysectomized rats with bovine pituitary extract, for two weeks, counteracted the effect of hypophysectomy, whereas treatment with bovine growth hormone was ineffective. Adrenalectomy produced similar though less extensive modification of Ca2+-induced swelling but failed to affect the MgATP-dependent mitochondrial contraction. Substrate oxidation by hypophysectomized or adrenalectomized rat mitochondria showed no modification of the energy-yielding mechanisms, capable of explaining the observed changes in mitochondrial swelling.

Decreased rate of ketone-body oxidation and decreased activity of D-3-hydroxybutyrate dehydrogenase and succinyl-CoA:3-oxo-acid CoA-transferase in heart mitochondria of diabetic rats.

Heart mitochondria from chronically diabetic rats ('diabetic mitochondria'), in metabolic State 3, oxidized 3-hydroxybutyrate and acetoacetate at a relatively slow rate, as compared with mitochondria from normal rats ('normal mitochondria'). No significant differences were observed, however, with pyruvate or L-glutamate plus L-malate as substrates. Diabetic mitochondria also showed decreased 3-hydroxybutyrate dehydrogenase and succinyl-CoA: 3-oxoacid CoA-transferase activities, but cytochrome content and NADH-dehydrogenase, succinate dehydrogenase, cytochrome oxidase and acetoacetyl-CoA thiolase activities proved normal. The decrease of 3-hydroxybutyrate dehydrogenase activity was observed in diabetic mitochondria subjected to different disruption procedures, namely freeze-thawing, sonication or hypoosmotic treatment, between pH 7.5 and 8.5, at temperatures in the range 6-36 degrees C, and in the presence of L-cysteine. Determination of the kinetic parameters of the enzyme reaction in diabetic mitochondria revealed diminution of maximal velocity (Vmax) as its outstanding feature. The decrease in 3-hydroxybutyrate dehydrogenase in diabetic mitochondria was a slow-developing effect, which reached full expression 2-3 months after the onset of diabetes; 1 week after onset, no significant difference between enzyme activity in diabetic and normal mitochondria could be established. Insulin administration to chronically diabetic rats for 2 weeks resulted in limited recovery of enzyme activity. G.l.c. analysis of fatty acid composition and measurement of diphenylhexatriene fluorescence anisotropy failed to reveal significant differences between diabetic and normal mitochondria. The Arrhenius-plot characteristics for 3-hydroxybutyrate dehydrogenase in membranes of diabetic and normal mitochondria were similar. It is assumed that the variation of the assayed enzymes in diabetic mitochondria results from a slow adaptation to the metabolic conditions resulting from diabetes, rather than to insulin deficiency itself.