An estimation of the parathyroid hormone secretion rate in vitamin D deficient rats

In an attempt to define the rate of endogenous secretion of parathyroid hormone in vitamin D deficiency, graded amounts of hormone were infused constantly into vitamin D deficient and vitamin D fed acutely thyroparathyroidectomized rats in a perfusion balance study. The dose of hormone needed to compensate for acute thyroparathyroidectomy was estimated. Serum levels of calcium and phosphorus, renal clearances of phosphorus and urinary excretion of cyclic AMP, each determined 16 hr after the surgery, were employed as parameters of the hormone effect. It was concluded that, in the condition of the perfusion balance study, the secretion rate of parathyroid hormone was 5.1-8.6 USP u/hr in the vitamin D deficient animals compared with 0.81-0.84 USP u/hr in the control.

Erythroblast kinetics in pernicious anaemia, erythroleukaemia and sideroblastic anaemia

DNA synthesis time (Ts) and 3H-thymidine labelling index (TLI) of erythroblasts have been determined in 25 patients with various types of haematologic disorders using in vitro double labelling method. No remarkable differences in both Ts and TLI were noted between haematologically normal subjects and patients with increased effective erythropoiesis (haemolytic anaemias), suggesting that the cell cycle time is not principally altered under the augmented erythropoiesis. In pernicious anaemia, Ts of basophilic erythroblasts was significantly shortened and TLI was elevated above normal. Normalization of erythropoiesis by vitamin B12 was associated with a transient increase of TLI in polychromatic erythroblasts, which was interpreted to reflect prevention of intramedullary premature death of basophilic megaloblasts. Erythroleukaemia showed a markedly prolonged Ts and lowered TLI indicating the presence of cells with prolonged cell cycle time. These findings contrasted to that of pernicious anaemia despite certain morphological as well as functional similarities. In idiopathic sideroblastic anaemia, prolongation of Ts was observed to a similar extent as erythroleukaemia, while TLI remained almost normal. In 2 cases with suspected erythroleukaemia presenting an intermediate clinical picture between erythroleukaemia and sideroblastic anaemia, Ts of basophilic erythroblasts was found to be prolonged along with modestly lowered TLI.

In vivo evidence for the intermediary role of 3',5'-cyclic AMP in parathyroid hormone-induced stimulation of 1alpha,25-dihydroxyvitamin D3 synthesis in rats

Teh stimulatory effect of parathyroid hormone (PTH) on renal 1alpha-hydroxylation of 25-hydroxyvitamin D3 (25-OH-D3) was studied in thyro-parathyroidectomized (TPTX), vitamin D-deficient rats into which bovine PTH, theophylline, cAMP or dibutyryl cAMP (dbcAMP) was constantly infused. The accumulation in plasma of 1alpha,25-dihydroxy-vitamin D3 [1alpha,25-(OH)2-D3], produced from 25-OH-D3, was enhanced by infusion of either cAMP (0.9 MUMOL/H) OR DBCAMP (1 mumol/h) to a level similar to the maximum obtained by PTH (i95--7.5 U/h) infusion. A submaximal dose (1 U/h) of PTH caused a similar extent of stimulation, when infused with theophylline. When either 2 mumol/h of cAMP or 7.5 U/h of bovine PTH was infused starting 18 h after TPTX, the accumulation of 1alpha,25-(OH)2-D3 in plasma was similarly restored withing 6 h to the level found in the sham-operated animals. These results strongly support the concept that cAMP plays an important intermediary role in the stimulation of 1alpha,25-(OH)2-D3 production induced by both exogenous and endogenous PTH.

Spin label studies on the human erythrocyte membrane. Two sites and two phases for fatty acid spin labels

Human erythrocytes, untreated and glutaraldehyde-treated, were spin labeled with three kinds of fatty acid labels, and their electron spin resonance (ESR) spectra were studied in detail at various temperatures. 1. The better spectral resolution could be obtained by packing the erythrocytes in a hematocrit capillary tube, because of the preferential parallel orientation of the cylindrical axes of erythrocyte-disc to the centrifugal axis. 2. It was demonstrated by the incorporation and the release of the labels that the membrane possessed two kinds of the fatty acid "sites": the tightly and weakly binding "sites" at the approximate molar ratio of 1:1. The rough estimates of the binding constants were obtained, which reproducibly varied with the blood donors over a period of a year. 3. The temperature dependency of the ESR spectra revealed the presence of two distinct phases, perhaps the solid and fluid phases. With lowering of the temperature, the fluid phase became more solid but the solid phase unchanged. The pretreatment of the erythrocytes with glutaraldehyde increased the amount of the frozen phase, corresponding to the decrease of the membrane flexibility.

Intestinal responses to hyperosmolar glucose infusion in dogs

Physiological and morphological changes of small intestine after hyperosmolar glucose infusions into canine jejunum were studied using in vivo perfusion model. Infusions of 40 ml of 50% and 20% glucose solution into the jejunal loops induced biphasic osmolar degression in the lumen. Osmolarity of jejunal venous blood was rapidly increased and maintained the maximal level (approximately 320 mOM/L). Blood flow to the jejunal loop was significantly increased after 50% glucose infusion compared to 5% glucose infusion. Most characteristic electron microscopic change of jejunal epithelial cell was pseudo-pod like process projected into the jejunal lumen, which was very similar to that of cholera.

Corticotropin-releasing factor-like activity in ACTH producing tumors

Corticotropin-releasing factor (CRF)-like activity in two different kinds of ACTH-producing tumors (human ectopic ACTH-producing colonic cancer and rat MtT/F4 tumor) was determined by an in vitro method using isolated normal rat pituitary cells. The ACTH content of the post mortem colonic cancer was 5.5 ng/g w.wt. The ACTH content of the medium of MtT/F4 tumor cells was 153+/-32 pg/10(5) cells. The ACTH content of MtT/F4 tumor cell suspensions was elevated with increasing doses of hypothalamic median eminence extract (HME). The response of MtT/F4 tumor cells to HME was suppressed by 1 mug/ml of dexamethasone. Extracts of colonic cancer, MtT/F4 tumor and HME produced elevation of the ACTH content of the medium of isolated rat pituitary cells. The CRF-like activities of two kinds of tumor extracts in multiple dilutions ran parallel to that of HME. The CRF-like activities were 0.037 HME equiv/mg w.wt in MtT/F4 tumor and 0.052 HME equiv/mg w.wt. in colonic cancer. These results demonstrated that CRF-like activity existed in these two kinds of ACTH-producing tumors.

Effects of parathyroid hormone on the accumulation of cyclic AMP in bone of vitamin D-deficient rats

The mechanism of skeletal refractoriness to parathyroid hormone (PTH) in vitamine D-deficient animals was studied in terms of the adenylate cyclase-cyclic AMP system in rat calvaria. In vitamin D-deficient, thyroparathyroidectomized rats, plasma calcium concentration was not elevated by iv administration of PTH, while responsiveness to the hormone was recovered within 24 h after a single dose (2.5 mug) of vitamin D3. In spite of the remarkable dependency of PTH on vitamin D for mobilization of calcium from bone, PTH stimulated adenylate cyclase activity in particulate bone cell fractions in vitro. PTH also enhanced the levels of cyclic AMP in the skeletal tissues of vitamin D-deficient rats in vivo and in vitro to an extent similar to those found in rats given 2.5 mug of D3. Administration of theophylline or dibutyryl cyclic AMP to the vitamin D-deficient rats did not cause any significant hypercalcemic effects, while these drugs enhanced plasma calcium concentration significantly in the rats given vitamin D3. These data strongly indicate that the cause of the skeletal refractoriness to PTH in vitamin D-deficient animals is not a defective activation of adenylate cyclase, but must be related to a later step or steps in the biochemical events leading to bone cell activation.

Hypothalamic-pituitary functions in patients with idiopathic pituitary dwarfism

To investigate hypothalamic-pituitary functions and the primary site of the lesion in idiopathic pituitary dwarfism, various pituitary function tests, especially the pituitary hormone responses to the hypophysiotropic hormones were studied in 23 patients with idiopathic pituitary dwarfism. A few cases showed slight responses of GH to GH stimulation tests. Gonadotropin deficiencies were most frequently noted among pituitary hormones. The basal levels and the responses of plasma LH and FSH to LH-RH test were diminished markedly in all of the cases except in 5 cases with isolated GH deficiency. Responses of LH and FSH to LH-RH improved markedly after a long term administration of LH-RH for a period of one month in 2 patients with gonadotropin deficiency. As to TSH axis, half of the cases accompanied hypothyroidism. However, the responses of TSH to TRH were normal in all of the cases regardless of the thyroid function. The basal levels and the responses of plasma cortisol and 11-deoxycortisol to the rapid metopirone test were also impaired in about half of the cases. Basal levels of plasma prolactin were normal in all of the cases and the responses of prolactin to TRH were normal in cases with normal thyroid function, but slightly delayed in cases with hypothyroidism. It is concluded from the above observations that the incidences of various pituitary hormone deficiencies were quite high in this disorder and hypophysiotropic hormone deficiencies may cause pituitary hormone deficiencies. Therefore, it is suggested that the primary site of the lesion in this disorder might be at the hypothalamus.