Effects of TSH on the adenylate cyclase-cAMP system and some parameters of intermediary metabolism were investigated in human thyroid carcinoma and adjacent normal thyroid tissue. Basal adenylate cyclase activity and cAMP concentrations were significantly higher in carcinomatous tissue. Basal [1-l4C]glucose oxidation, 32Pi incorporation into phospholipids, and organification of iodide were similar in both tissues. Stimulation of cAMP by TSH was significantly greater in normal compared to carcinomatous tissue. In neither tissue was there a good correlation between TSH stimulation of adenylate cyclase activity and cAMP concentrations. The TSH stimulation of 32Pi incorporation into phospholipids by TSH was significantly greater in normal tissue. The mean effect of TSH on iodide organification and glucose oxidation was similar in normal and carcinomatous tissue. Although specific binding of TSH was demonstrated in both normal and carcinomatous tissue, it did not correlate very well with stimulation of adenylate cyclase activity. Hormones other than TSH also augmented adenylate cyclase activity in two of the carcinomas. In individual patients, the relative responsivity of carcinomatous tissue compared to normal was not always consistent when all of the metabolic parameters were considered.
Abstract In an attempt to study the effects of several substances on intracellular cyclic adenosine 3′:5′-monophosphate (cAMP) concentration in tumor cells, lymphoma cells were incubated with biogenic amines (histamine, norepinephrine, epinephrine, and isoproterenol), prostaglandin E1 (PGE1), and Vinca alkaloids (vincristine and vinblastine). All substances tested increased intracellular cAMP in the presence of theophylline. Combined administration of Vinca alkaloid with biogenic amines or PGE1 produced an additive increase of cAMP in lymphoma cells. Vinca alkaloids depressed cAMP phosphodiesterase activity, but this depression was too weak to explain an increase of cAMP. In lymphoma cell homogenate, biogenic amines and PGE1 increased cAMP but Vinca alkaloids failed to do so, suggesting destruction of the receptor and/or transducer mechanism for Vinca alkaloids by homogenization. The effect of biogenic amines, PGE1, and Vinca alkaloids on cAMP was depressed by pretreatment of lymphoma cells with phospholipases C and A2. In vivo treatment of lymphoma cells with vinblastine gradually reduced the receptor and/or transducer mechanism for Vinca alkaloids, PGE1, and isoproterenol. It is suggested that Vinca alkaloids elevated cAMP concentration in lymphoma cells by acting on the plasma membrane. The receptor for Vinca alkaloids is distinct from those for biogenic amines and PGE1.
In an attempt to study the nature, magnitude, duration, and temporal sequence of hypothalamo-pituitary-thyroid responses to cold, intact guinea pigs and rats, guinea pigs with midbrain transection or intact rats injected with 3-adrenergic blocking agent were exposed to cold (4 C) for 30 min. For comparison, TSH, thyrotropin releasing factor (TRF), and three hormones were administered to intact mice and guinea pigs or midbrain-transected guinea pigs. An increase of intracellular colloid droplets in the thyroid was apparent within 10 min, maximal at 30 min, and gradually subsided by 120 min when the animals were acutely exposed to cold. Propranolol increased intracellular colloid droplet formation and this effect was additive to that of cold. Midbrain transection completely abolished an increase of colloid droplets in response to cold, without affecting pituitary responsiveness to TRF. Since this increase of colloid droplet was produced by TSH and TRF but not by hydrocortisone, norepinephrine, and epinephrine, it is suggested that the hypothalamus is stimulated by nervous impulses originating from peripheral cold receptors to secrete TRF. (Endocrinology90: 538, 1972)
An alignment of 5 amino acids in the Escherichia coli proline carrier (G328-A366-L371-GR376) is common in the amino acid sequences of several Na+ symport carriers, and it has been proposed as the putative sodium binding motif (Deguchi, Y., Yamato, I., and Anraku, Y. (1990) J. Biol. Chem. 265, 21704-21708). To determine whether these amino acids are essential for Na+ symport activity as the Na+ binding site, one of the amino acids in this alignment, Arg-376, which is the only positively charged amino acid in the innermost part of the predicted membrane-spanning regions, was changed to either lysine, glutamine, or glutamic acid by oligonucleotide dependent site-specific mutagenesis. The transport and binding activities of the proline of the R376K mutant carrier were not detected at all. The activities of the other mutant carriers for uptake and binding of proline were as high as those of the wild-type carrier. These two mutant carriers were as sensitive to the proline analogue azetidine-2-carboxylate and to N-ethylmaleimide as the wild-type carrier, indicating that they have the same properties as the wild-type. The amounts of the carrier proteins expressed from these mutated putP genes were similar to that from the wild-type gene. These results imply that the Arg-376 in the proline carrier does not reside at the sodium binding site, suggesting that the similar alignment found in the amino acid sequences of several Na+ symport carriers is not essential for the transport or binding activities, although this similar alignment may have some relevance to the structure of the Na+ symporter. Furthermore, that the only Arg residue in the middle part of the predicted membrane-spanning regions is dispensable for the energy coupling activity indicates a unique difference of the coupling mechanism from the other secondary active transport systems, such as that of the lactose permease and the tetracycline/H+ antiporter.
Synthetic TRH stimulated the oxidation of glucose-1-14C to 14CO2 at a concentration of 2.5 μg/ml in porcine anterior pituitary slices. This stimulation was not observed in porcine posterior pituitary slices or in rat hemipituitaries. TRH also stimulated the production of 14CO2 from glucose-U-14C in the porcine anterior pituitary. This stimulatory effect of TRH on glucose oxidation was blocked by thyroxine added to the incubation medium at a concentration of 10 μg/ml.
In a middle-aged woman with virilizing adenoma, 2 mg dexamethasone increased urinary excretion of 17-ketosteroids (17-KS) and 17-hydroxycorticosteroids, whereas 8 mg dexamethasone increased urinary excretion only of 17-KS. With discontinuation of dexamethasone, 17-KS excretion returned to the predexamethasone level. Dexamethasone depressed the basal level of cAMP synthesis and basal testosterone production by the normal adrenal tissue in vitro. Dexamethasone also depressed the increase of cAMP produced by ACTH in the normal tissue. In contrast, dexamethasone increased basal cAMP synthesis and stimulated testosterone secretion in the tumor tissue. ACTH and dexamethasone were additive in their effects on cAMP and testosterone in the tumor tissue. It is suggested that dexamethasone acted directly on the adrenal tumor to stimulate steroid secretion in this patient. (J Clin Endocrinol Metab48: 660, 1979)
