Interferon-gamma overcomes glucocorticoid suppression of cachectin/tumor necrosis factor biosynthesis by murine macrophages.

Glucocorticoids almost completely inhibit the synthesis by isolated macrophages of cachectin/tumor necrosis factor (TNF), a cytokine implicated as a major endogenous mediator of septic shock. Despite this in vitro effectiveness, the clinical use of glucocorticoids has failed to demonstrate any clear benefit in the treatment of septic shock. In an effort to understand what other mechanisms might play a role in the patient with sepsis, we examined the effect of interferon-gamma (IFN gamma) on the synthesis of cachectin/TNF. We show here that IFN gamma, although unable by itself to induce cachectin/TNF synthesis, enhanced the endotoxin-induced production of cachectin/TNF in vitro. Furthermore, IFN gamma overcame the inhibition of cachectin/TNF synthesis caused by the glucocorticoid, dexamethasone. These effects of IFN gamma were accounted for by increased levels of cachectin/TNF mRNA. The in vivo implications of these studies are discussed with emphasis on their relevance in human sepsis.

Impaired diurnal adrenal rhythmicity restored by constant infusion of corticotropin-releasing hormone in corticotropin-releasing hormone-deficient mice.

The normal pattern of daily glucocorticoid production in mammals requires circadian modulation of hypothalamicpituitary-adrenal axis activity. To assess both the factors responsible for imparting this diurnal profile and its physiologic importance, we have exploited corticotropin-releasing hormone (CRH)-deficient mice generated by homologous recombination in embryonic stem cells. CRH-deficient mice have lost normal circadian variations in plasma ACTH and glucocorticoid while maintaining normal circadian locomotor activity. Constant peripheral infusion of CRH produced marked diurnal excursions of plasma glucocorticoid, indicating that CRH acts in part as a permissive factor for other circadian modulators of adrenocortical activity. The presence of atrophic adrenals in CRH-deficient mice without an overt deficit in basal plasma ACTH concentration suggests that the diurnal increase in ACTH is essential to maintain normal adrenal function.

Altered stress-induced anxiety in adenylyl cyclase type VIII-deficient mice.

Stress results in alterations in behavior and physiology that can be either adaptive or maladaptive. To define the molecular pathways involved in the response to stress further, we generated mice deficient (KO) in the calcium-stimulated adenylyl cyclase type VIII (AC8) by homologous recombination in embryonic stem cells. AC8 KO mice demonstrate a compromise in calcium-stimulated AC activity in the hippocampus, hypothalamus, thalamus, and brainstem. Hippocampal slices derived from AC8 KO mice fail to demonstrate CA1-region long-term depression after low-frequency stimulation, and AC8 KO mice also fail to activate CRE-binding protein in the CA1 region after restraint stress. To define the behavioral consequences of AC8 deficiency, we evaluated AC8 KO mice in the elevated plus-maze and open field. Although naive AC8 KO mice exhibit indices of anxiety comparable with that of wild-type mice, AC8 KO mice do not show normal increases in behavioral markers of anxiety when subjected to repeated stress such as repetitive testing in the plus-maze or restraint preceding plus-maze testing. These results demonstrate a novel role for AC8 in the modulation of anxiety.

Expression of the arginine vasopressin gene in response to salt loading in oxytocin gene knockout mice.

Accumulating evidence suggests that both oxytocin and arginine vasopressin (AVP) are vital components in the regulation of body fluid balance. However, the physiological role of oxytocin and possible cooperative interactions between oxytocin and AVP in sodium balance remain obscure, even though recent studies using oxytocin knockout (OTKO) mice suggested that oxytocin may contribute to the regulation of salt appetite. In the present study, we examined the effects of salt loading (drinking 2% NaCl for 5 days) on the expression of the AVP gene in the paraventricular (PVN) and supraoptic nuclei (SON) of wild-type, OTKO and heterozygous littermates using in situ hybridization histochemistry. In addition, the effects of salt loading on the expression of the oxytocin gene were also examined in wild-type and heterozygous mice. Under the non salt-loaded condition, the levels of AVP mRNA in the PVN and SON of OTKO mice were significantly decreased compared to those in wild-type mice. Nevertheless, the up-regulation of the expression of the AVP gene in response to salt loading was preserved in OTKO mice. The degree of the up-regulation in OTKO mice tended to be greater compared to those in wild-type mice, suggesting compensatory up-regulation of the expression of the AVP gene in OTKO mice after salt loading. The basal levels of oxytocin mRNA in the PVN and SON of heterozygous mice were significantly lower than those in wild-type mice. Salt loading caused an increase of oxytocin mRNA levels in the PVN and SON of both wild-type and heterozygous mice. The ratios of increase of oxytocin mRNA levels were very similar between wild-type and heterozygous mice, suggesting that the single remaining oxytocin gene in heterozygous mice responds normally to an osmotic cue. Finally, salt loading tended to increase the serum concentration of sodium regardless of genotype, and there were no genotype differences in both the control and salt-loaded groups. These results suggest ways in which oxytocin may play a cooperative role together with AVP in the regulation of sodium balance.

Oxytocin modulates the onset of murine parturition by competing ovarian and uterine effects.

Recent analysis of mice deficient in both oxytocin (OT) and cyclooxygenase-1 has shown that OT exerts significant effects on both the ovarian corpus luteum and the uterine myometrium during pregnancy. To better define the roles of OT during pregnancy, we evaluated OT action and OT receptor regulation in wild-type and OT-deficient knockout (KO) mice. Continuous infusion of OT revealed that OT can either delay labor at low doses or initiate preterm labor at high doses. The infusion rates of OT necessary for these effects were reduced in OT KO mice. The dose of OT that delayed labor also delayed the normal decrease in plasma progesterone late in gestation, implicating a primary effect on the corpus luteum. Consistent with this hypothesis, luteal OT receptor expression exceeded that of the myometrium until luteolysis occurred. We propose that the downregulation of OT receptors in the corpus luteum and induction of OT receptors in the myometrium serve to shift the predominant consequence of OT action during murine pregnancy from labor inhibition to labor promotion.