Pseudo vitamin D deficiency rickets in pigs: in vitro measurements of renal 25-hydroxycholecalciferol-1-hydroxylase activity

Mechanisms that lead to disease of the endocrine system in animals

Endocrine glands are collections of specialized cells that synthesize, store, and release their secretions directly into the blood stream. They are sensing and signalling devices located in the extracellular fluid compartment and are capable of responding to changes in the internal and external environments to coordinate a multiplicity of activities that maintain homeostasis. Diseases of the endocrine system are encountered in many animal species and present challenging diagnostic problems. The major pathogenic mechanisms responsible for disturbances in endocrine function include: 1) primary hyperfunction of an endocrine gland; 2) secondary hyperfunction; 3) primary hypofunction of an endocrine gland; 4) secondary hypofunction; 5) endocrine hyperactivity secondary to diseases of other organs; 6) hypersecretion by nonendocrine tumors of hormone-like substances; 7) failure of fetal endocrine function; 8) endocrine dysfunction due to failure of target cell response; 9) endocrine dysfunction resulting from abnormal degradation of hormone; and 10) iatrogenic syndromes of hormone-excess. For each major category, several specific disease problems have been selected to illustrate the morphologic and functional changes that characterize the response of a particular endocrine gland to disruption of function.

Endocrine control and disturbances of calcium and phosphate metabolism in children

Most disorders of extracellular calcium and phosphate metabolism in childhood can be attributed to primary increased or decreased secretion/action of 1,25-dihydroxyvitamin D3 and parathyroid hormone or primary increased or decreased urinary excretion of phosphate and calcium. Based on this pathogenetic classification the most important diseases related to calcium and phosphate metabolism will be discussed.

Absence of renal 25-hydroxycholecalciferol-1-hydroxylase activity in a pig strain with vitamin D-dependent rickets

Cholecalciferol-1-hydroxylase activities were estimated in renal cortex homogenates and mitochondrial preparations from three groups of 6- to 12-week-old pigs. Five animals suffering from an inherited form of vitamin D-deficiency rickets showed symptoms of florid rickets when used for this study. Six pigs were normocalcemic heterozygous litter mates of the rachitic strain and three pigs were normal controls (German land-race and wild pigs). The renal cortex homogenates and mitochondrial preparations were incubated for 5-30 min at 37 degrees C with 25-(26-27-methyl-3H) OHD3 as substrate. 1,25(OH)2D3 was subsequently identified in normal phase (Zorbax-Sil) and reversed phase (Zorbax-ODS) HPLC eluates. 1-hydroxylase activities were demonstrated in both normal controls and heterozygote offspring and were ten times above minimum detectability of the assay. The km was 255 +/- 74 (SD) and 278 +/- 85 nmol X 1(-1) in controls and heterozygote offspring, respectively. The Vmax in the two groups was between 0.11 and 0.794 and decreased with age of the animals. Km and Vmax did not differ between the two groups. In homozygous, hypocalcemic rachitic animals no 1-hydroxylase activity was detectable in either homogenates or mitochondrial preparations. Addition of kidney homogenate from a rachitic animal to a homogenate from a normal pig did not specifically depress 1-hydroxylase activity in the mixture. Treatment of rachitic pigs with 1.0 microgram/day of 1,25(OH)2D3 for 4 weeks also had no effect on 1-hydroxylase activity. It is concluded that the rachitic pigs suffer from an inborn error of renal 1,25(OH)2D3 production.(ABSTRACT TRUNCATED AT 250 WORDS)