The effect of thyroid hormone and a long-acting somatostatin analogue on TtT-97 murine thyrotropic tumors.

Thyroid hormone inhibits thyrotropin (TSH) production and thyrotrope growth. Somatostatin has been implicated as a synergistic factor in the inhibition of thyrotrope function. We have previously shown that pharmacological doses of thyroid hormone (levothyroxine [LT4]) inhibit growth of murine TtT-97 thyrotropic tumors in association with upregulation of somatostatin receptor type 5 (sst5) mRNA and somatostatin receptor binding. In the current study, we examined the effect of physiological thyroid hormone replacement alone or in combination with the long-acting somatostatin analogue, Sandostatin LAR, on thyrotropic tumor growth, thyrotropin growth factor-beta (TSH-beta), and sst5 mRNA expression, as well as somatostatin receptor binding sites. Physiological LT4 replacement therapy resulted in tumor shrinkage in association with increased sst5 mRNA levels, reduced TSH-beta mRNA levels and enhanced somatostatin receptor binding. Sandostatin LAR alone had no effect on any parameter measured. However, Sandostatin LAR combined with LT4 synergistically inhibited TSH-beta mRNA production and reduced final tumor weights to a greater degree. In this paradigm, Sandostatin LAR required a euthyroid status to alter thyrotrope parameters. These data suggest an important interaction between the somatostatinergic system and thyroid hormone in the regulation of thyrotrope cell structure and function.

Cloning of the mouse somatostatin receptor subtype 5 gene: promoter structure and function.

Somatostatin is a peptide hormone whose actions are mediated by five somatostatin receptor subtypes (sstl-5). In the pituitary, somatostatin inhibits TSH release from thyrotropes and GH release from somatotropes. We have shown that sst5 transcripts and protein are induced by thyroid hormone in TtT-97 thyrotropic tumors. To map sequences responsible for promoter activity in pituitary cells, we cloned the mouse sst5 coding region of 362 amino acids and 12 kb of upstream DNA. Initial transfection studies in TtT-97 or GH3 cells mapped high levels of basal promoter activity to a 5.6-kb fragment upstream of the translational start, whereas shorter genomic fragments had low activity. To identify the transcriptional start site we used 5' RACE with TtT-97 poly A+ RNA and a sst5 antisense coding region primer. Sequence comparison between the complementary DNA and the gene revealed that the mouse sst5 gene contains 3 exons and 2 introns. The entire coding region was contained in exon 3. Two differently sized RACE products demonstrated alternate exon splicing of two untranslated exons in TtT-97 cells. A promoter fragment from -290/+48 linked to a luciferase reporter demonstrated 600- and 900-fold higher activity over a promoterless control in GH3 mammosomatotropes and TtT-97 thyrotropes, respectively, whereas a larger fragment extending to -6400 exhibited no additional promoter activity. Cloning of the sst5 gene will facilitate the mapping of basal and regulated responses at the transcriptional level.

Systemic and renal hemodynamic changes in the luteal phase of the menstrual cycle mimic early pregnancy.

Blood pressure decreases during early pregnancy in association with a decrease in peripheral vascular resistance and increases in renal plasma flow and glomerular filtration rate. These early changes suggest a potential association with corpora lutea function. To determine whether peripheral vasodilation occurs following ovulation, we studied 16 healthy women in the midfollicular and midluteal phases of the menstrual cycle. A significant decrease in mean arterial pressure in the midluteal phase of the cycle (midfollicular of 81.7 +/- 2.0 vs. midluteal of 75.4 +/- 2.3 mmHg, P < 0.005) was found in association with a decrease in systemic vascular resistance and an increase in cardiac output. Renal plasma flow and glomerular filtration rate increased. Plasma renin activity and aldosterone concentration increased significantly in the luteal phase accompanied by a decrease in atrial natriuretic peptide concentration. Serum sodium, chloride, and bicarbonate concentrations and osmolarity also declined significantly in the midluteal phase of the menstrual cycle. Urinary adenosine 3',5'-cyclic monophosphate (cAMP) excretion increased in the luteal compared with the follicular phase, whereas no changes in urinary cGMP or NO2/NO3 excretion were found. Thus peripheral vasodilation occurs in the luteal phase of the normal menstrual cycle in association with an increase in renal plasma flow and filtration. Activation of the renin-angiotensin-aldosterone axis is found in the luteal phase of the menstrual cycle. These changes are accompanied by an increase in urinary cAMP excretion indicating potential vasodilating mediators responsible for the observed hemodynamic changes.

Factors that modulate inescapable shock-induced reductions in daily activity in the rat.

Most behavioral and neurochemical changes produced by inescapable shock dissipate in 1-3 days. However, daily running activity is depressed for 14-42 days following one to three sessions of inescapable shock. In the present experiments, we sought to determine whether factors known to be important in the development of the short-term effects of exposure to inescapable shock would also be important in the production of the long-term effect of inescapable shock on daily activity. Three factors were examined: a) the escapability of the shock; short-term behavioral changes generally do not occur if the shock is escapable; b) naltrexone pretreatment; the opioid antagonist naltrexone typically prevents many of the short-term behavioral sequelae of inescapable shock; c) treatment with the anxiogenic beta-carboline FG-7142; administration of this compound alone frequently mimics inescapable shock in its ability to transiently disrupt behavior. The inescapable shock-induced reduction in daily activity did not depend upon escapability of the stressor. In addition, naltrexone did not prevent and FG-7142 did not induce the reduction in daily activity associated with stressor exposure.

Adinazolam both prevents and reverses the long-term reduction of daily activity produced by inescapable shock.

The behavioral consequences of exposure to stressors such as inescapable shock are usually quite transitory if testing is conducted in an environment different from that in which the stressor was administered. Daily running activity is an exception in that it remains depressed for several weeks following experience with inescapable shock. In the present experiments we found the administration of the triazolbenzodiazepine adinazolam able to both reduce this long-term activity reduction produced by inescapable shock when acutely administered before the inescapable shock, and to reverse the effect when chronically administered after the inescapable shock. Classic 1,4-benzodiazepines such as diazepam have been able to prevent such effects when acutely administered before inescapable shock, but cannot reverse these effects when provided after the inescapable shock. Conversely, classic antidepressants such as desipramine have been unable to prevent these behavioral effects when given before inescapable shock in acute form, but can reverse the effects with chronic administration following the inescapable shock. Our observations that adinazolam can both prevent and reverse the effects of inescapable shock are consistent with reports that this agent has both anxiolytic and antidepressant effects in clinical use.

Monoamine neurotransmitters and metabolites during the estrous cycle, pregnancy, and the postpartum period.

A wide variety of behavioral changes in the female rat have been associated with the estrous cycle, pregnancy, and the postpartum period and their accompanying hormonal fluctuations. Since monoamine systems have been implicated in the control of these behaviors, the present study examined the tissue concentrations of norepinephrine (NE), dopamine (DA), and serotonin (5HT) and their primary metabolites dihydroxyphenylglycol (DHPG), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5HIAA) in the anterior cerebral cortex, hippocampus, and cerebellum during the estrous cycle, late pregnancy, and the early postpartum period. Results show no significant differences in neurotransmitter or metabolite levels during the estrous cycle in any of the three brain regions examined. However, profound differences were observed between samples from late pregnancy, early postpartum, and the estrous cycle. In general, NE and 5HT levels in all three brain regions fell from normal values during late pregnancy and rose in the early postpartum period; levels of their metabolites rose in postpartum samples. Conversely, DA levels were elevated in late pregnancy and depressed in the early postpartum period in anterior cortex, while DOPAC levels were depressed in both late pregnancy and the early postpartum period. The finding of changes in monoamine metabolism associated with pregnancy and its termination could be important in understanding the increased susceptibility to affective illness in women during the postpartum period.

Aerospace thermal mapping applications of liquid crystals.

The ability of liquid crystals to reveal small temperature gradients has resulted in studies of their utility in the thermal testing of aerospace materials and components. Reported here are tests to reveal anomalous conditions at or near the surface of a variety of materials. Also described are low cost techniques for performing thermal mapping on large areas. Advantages and disadvantages of thermal mapping with liquid crystals are summarized.