Lack of involution of hyperplastic parathyroid glands in dogs: adaptation via a decrease in the calcium stimulation set point and a change in secretion profile.
This study analyzes the parathyroid function in four dogs before and after 2 years of a low-calcium, high-sodium, vitamin D-deficient diet and the involution of the same function following (1) correction of dietary calcium deficiency and administration of i.v. 1,25-(OH)2D (0.25 micrograms twice per day) during 1 month, (2) after an additional month of normal dog chow supplemented with oral vitamin D (25 micrograms per day), and, finally, (3) after 5 and 17 months of a diet with normal levels of calcium and vitamin D. The parathyroid function was evaluated through i.v. infusion of CaCl2 and Na2 EDTA with measurement of intact (I) and carboxyl-terminal (C) immunoreactive parathyroid hormone (iPTH). The C-iPTH/I-iPTH ratio was calculated to assess the modulation of molecular forms of iPTH induced by the various treatments. The 2 years of calcium and vitamin D deprivation lowered ionized calcium (1.23 +/- 0.04, p < 0.05) and 25-OHD (4.02 +/- 2.06 nM, p < 0.005) and tended to decrease 1,25-(OH)2D (80.8 +/- 8.6 pM); it increased basal I- and C-iPTH levels approximately eightfold (I-iPTH, 40.2 +/- 20.7, p < 0.05; C-iPTH, 185.4 +/- 94.9, p < 0.05) and stimulated I-iPTH (60.2 +/- 23.0 pM, p < 0.05) and C-iPTH (239.6 +/- 80.7 pM, p < 0.05) fivefold. A greater rise in nonsuppressible I-iPTH levels than in C-iPTH levels led to a decreased C-iPTH/I-iPTH ratio in hypercalcemia (12.5 +/- 2.8 versus 27.8 +/- 6.05 pM, p < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)
Cloutier
M
M
Centre de recherche clinique André-Viallet, Hôpital Saint-Luc, Montreal, Quebec, Canada.
Brossard
J H
JH
Gascon-Barré
M
M
D'Amour
P
P
D000222:Adaptation, Physiological; D000284:Administration, Oral; D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000097:blood / Q000172:deficiency / Q000378:metabolism*; D004285:Dogs; D005260:Female; D006887:Hydroxycholecalciferols / Q000008:administration & dosage / Q000097:blood; D006961:Hyperparathyroidism / Q000473:pathology / Q000503:physiopathology*; D006965:Hyperplasia; D010280:Parathyroid Glands / Q000187:drug effects / Q000502:physiology*; D010281:Parathyroid Hormone / Q000378:metabolism*; D012982:Sodium, Dietary / Q000008:administration & dosage; D014807:Vitamin D / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D014808:Vitamin D Deficiency / Q000503:physiopathology
D006887:Hydroxycholecalciferols; D010281:Parathyroid Hormone; D012982:Sodium, Dietary; D014807:Vitamin D; D002118:Calcium