Altered TSH levels associated with increased serum 1,25-dihydroxyvitamin D3: a possible link between thyroid and parathyroid disease.
The physiologic relationship between the thyroid and parathyroid glands remains poorly understood. A high incidence of coexistent thyroid disease and primary hyperparathyroidism has been well documented. Elevation of serum 1,25-dihydroxyvitamin D3 (vitamin D) has been detected in some patients with primary hyperparathyroidism. A report of specific binding sites and uptake of vitamin D by the thyrotrophs of the anterior pituitary indicates that vitamin D may modulate production or secretion of thyroid-stimulating hormone (TSH). To test this concept, we investigated the influence of elevated serum levels of vitamin D on basal and stimulated TSH. Vitamin D was administered by subcutaneously implanted sustained-release pellets at four dosages. Thyrotropin releasing hormone (TRH) stimulation tests were performed at time zero, 72 hours, 1 week, 2 weeks, and 5 weeks. Animals administered vitamin D became significantly hypercalcemic and demonstrated elevations of vitamin D, which peaked at 72 hours and remained elevated for 2 weeks after pellet implantation. TRH-stimulated TSH levels were significantly elevated at 72 hours and at 1 week and returned to normal after 5 weeks. Parathyroid hormone levels were suppressed at 72 hours and at 1 week and displayed significant elevation at 2 weeks. These results provide in vivo evidence for an interaction and a possible regulatory role of 1,25 on pituitary TSH secretion and parathyroid function.
Smith
M A
MA
Department of Surgery, Loyola University Stritch School of Medicine, Maywood, Ill.
McHenry
C
C
Oslapas
R
R
Hofmann
C
C
Hessel
P
P
Paloyan
E
E
D000818:Animals; D002117:Calcitriol / Q000097:blood* / Q000494:pharmacology; D008297:Male; D008954:Models, Biological; D010279:Parathyroid Diseases / Q000150:complications*; D051381:Rats; D011919:Rats, Inbred Strains; D013959:Thyroid Diseases / Q000150:complications*; D013972:Thyrotropin / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D002117:Calcitriol