Effects of hypophysectomy and prolactin on calcium regulation in the red-spotted newt, Notophthalmus viridescens

Amphibian parathyroids: morphological and functional aspects

Amphibians living partially or totally in a terrestrial environment are the first tetrapods to possess parathyroid glands. Purely aquatic amphibians and amphibian larvae lack these endocrine glands. The parathyroids develop at the time of metamorphosis. The parathyroid glands in caecilians consist of a single cell type, that of urodeles may be composed of basal (supporting) cells and suprabasal (chief) cells, and that of anurans of small and large chief cells. Parathyroid glands of caecilians and anurans lack connective tissue, blood vessels, and nerves. The parathyroid cells become activated in response to decreased blood calcium concentration and undergo changes indicating increased parathyroid hormone secretion. Increased blood calcium concentration suppresses secretory activity. Usually, parathyroidectomy elicits hypocalcemia in most amphibians. Such operations have no effect in lower urodeles. Parathyroid hormone administration provokes hypercalcemia in most amphibians. The parathyroids of caecilians have not been studied in detail. The urodeles and anurans exhibit seasonal changes in the parathyroid glands. These changes may be initiated by environmental stimuli such as light, temperature, or alterations in blood calcium levels caused by natural hibernation.

The occurrence of chronic hypocalcemia following parathyroidectomy in the green frog, Rana clamitans

The plasma calcium concentrations of parathyroidectomized male specimens of the green frog, Rana clamitans, were monitored for 44 or 62 weeks. Plasma total and ionized calcium levels of the parathyroidectomized animals decreased 31-53% within 3 days, continued to fall to approximately 50% of the preoperative levels by Weeks 3-9, and remained at these low levels for the duration of the experiments. Plasma sodium, pH, and hematocrit levels were unchanged. The chronic hypocalcemia resulted in tetanic spasms in all of the long-term parathyroidectomized animals and in the death of most of the long-term parathyroidectomized animals. Thus, in the green frog the presence of the parathyroid gland is required for maintenance of blood calcium levels and for survival.

Effects of parathyroid hormone on cyclic-AMP concentrations of in vitro Necturus maculosus gastric antrum

The effects of bovine parathyroid hormone (bPTH1-84) on the stimulation of intracellular cyclic-AMP [cAMP] were investigated in an in vitro preparation of Necturus maculosus antral mucosa. When the antrum was exposed to 1, 5, 10, or 100 nM bPTH1-84, there was an approximately 2-fold nonlinear increase in tissue [cAMP] over basal values. The pretreatment of the antral mucosa with 1 mM isobutylmethylxanthine (IBMX, a phosphodiesterase inhibitor) increased with detectability of mucosal [cAMP]. The addition of 1, 5, 10, or 100 nM bPTH1-84 to tissues pretreated with IBMX resulted in an approximately 3.5-fold linear increase in mucosal [cAMP] over basal values. The time course of the generation of mucosal cAMP to 10 nM bPTH1-84 resulted in a small but significant transient increase at 2.5 min after the addition of bPTH1-84 but no change in the medium [cAMP]. In tissues pretreated with 1 mM IBMX the response to 10 nM bPTH1-84 was a large biphasic increase of [cAMP] at 2.5 min that progressively declined to near basal values by 15 min. There was also a significant sustained increase in the [cAMP] in the bathing medium at 2.5 min of tissues pretreated with IBMX followed by 10 nM bPTH1-84. These results suggest the presence of an adenylate cyclase that can be activated by a mammalian bPTH1-84 in elevating intracellular cAMP levels in the N. maculosus antral mucosa.