Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) influence hair follicles through paracrine and intracrine routes. There is significant evidence that PTH and PTHrP influence the proliferation and differentiation of hair follicle cells. The PTH/PTHrP receptor signalling plays an important role in the hair follicle cycle and may induce premature catagen-telogen transition. Transgenic mice with an overexpression or blockade (PTH/PTHrP receptor knockout mice) of PTHrP activity revealed impaired or increased hair growth, respectively. Some findings also suggest that PTHrP may additionally influence the hair cycle by inhibiting angiogenesis. Antagonists of the PTH/PTHrP receptor have been shown to stimulate proliferation of hair follicle cells and hair growth. A hair-stimulating effect of a PTH/PTHrP receptor antagonist applied topically to the skin has been observed in hairless mice, as well as in mice treated with cyclophosphamide. These data indicate that the PTH/PTHrP receptor may serve as a potential target for new (topical) hair growth-stimulating drugs, especially for chemotherapy-induced alopecia.

Milk-alkali syndrome (MAS), characterized by renal failure, metabolic alkalosis and hypercalcemia, is a severe and life-threatening complication of the treatment of hypoparathyroidism. The clinical course is often sudden and is not preceded by any prodromal symptoms. Occurrence does not depend on the duration of hypoparathyroidism treatment, although it is closely related to the applied therapy, especially the dose of calcium carbonate and active vitamin D preparations. Drugs influencing the glomerular filtration rate (angiotensin receptor blockers, sartans, aldosterone receptor antagonists, thiazide diuretics), lack of adequate routine control, changing the calcium carbonate supplementation, dehydration, a diet rich in pH-basic foods (i.e. vegetarian diet), pregnancy and other associated conditions are listed among the factors triggering MAS. A higher calcium carbonate dose is directly associated with an increased risk of milk-alkali syndrome. In case of a high calcium demand it is necessary to control renal function and monitor the level of calcium in the serum more frequently, aiming for the lower end of the reference range. If MAS has been confirmed or if there are alarming neurological symptoms suggestive of hypercalcemia, the patient must be sent to the hospital immediately. Treatment of MAS involves: discontinuation of calcium and vitamin D supplementation, and intravenous infusion of normal saline solution to eliminate volume deficiencies and to achieve forced diuresis while maintaining proper fluid balance. As soon as there is improvement in the patient's clinical condition, it is necessary to begin the treatment of comorbidities increasing the risk of renal failure or alkalosis (i.e. vomiting, diarrhea).