Forced and unforced ocean temperature changes in Atlantic and Pacific tropical cyclogenesis regions.

Previous research has identified links between changes in sea surface temperature (SST) and hurricane intensity. We use climate models to study the possible causes of SST changes in Atlantic and Pacific tropical cyclogenesis regions. The observed SST increases in these regions range from 0.32 degrees C to 0.67 degrees C over the 20th century. The 22 climate models examined here suggest that century-timescale SST changes of this magnitude cannot be explained solely by unforced variability of the climate system. We employ model simulations of natural internal variability to make probabilistic estimates of the contribution of external forcing to observed SST changes. For the period 1906-2005, we find an 84% chance that external forcing explains at least 67% of observed SST increases in the two tropical cyclogenesis regions. Model "20th-century" simulations, with external forcing by combined anthropogenic and natural factors, are generally capable of replicating observed SST increases. In experiments in which forcing factors are varied individually rather than jointly, human-caused changes in greenhouse gases are the main driver of the 20th-century SST increases in both tropical cyclogenesis regions.

Circadian fluctuations in plasma corticosterone, corticosterone-binding activity and total protein in male rats: possible disruption by serial blood sampling.

Male rats were bled serially every 6 h for 48 consecutive hours. Plasma so obtained was assayed for corticosterone (B), corticosterone-binding activity (CBA) and total plasma protein (TPP). Although the averaged data indicated a significant circadian rhythm in plasma B, inspection of the circadian changes in individual animals showed that 40% had irregular or aberrant patterns of plasma B. Additionally, circadian fluctuations in plasma CBA were approximately 3-fold lower in magnitude than previously reported, and there was no significant circadian change in TPP. Running wheel activity during the 48 h blood sampling period decreased by over 50% indicating that the serial sampling procedure caused disruption of the activity cycle. However, the majority of wheel-running activity occurred during the dark portion of the day-night cycle. Because circadian fluctuations in plasma proteins, including corticosteroid binding globulin (CBG), may be directly related to changes in locomotor activity, it is suggested that the attenuation of circadian changes in CBA and TPP were due to disruption of the daily cycle of locomotor activity. The abnormal circadian patterns in plasma B observed in some animals also may have been caused by disruption of the activity cycle in spite of the fact that the rats did not appear to be stressed as evidenced by concentrations of plasma B that were well within the normal range.

Rapid corticosterone pulses: confirmation by an alleged disconfirmation?

Data from a paper reporting a failure to confirm our report of rapid corticosterone pulses and suggesting that our data were artifactual were reanalyzed and reevaluated. It is shown that these data actually appear to confirm our original report. Artifacts in their procedure tend to introduce smearing that minimizes the observed effect. In addition, their method of data presentation combined with the lack of appropriate data analysis apparently led to their failure to draw the proper conclusions.

Rapid corticosterone pulses.

If micro-sampling techniques are used in conjunction with a highly sensitive radioimmunoassay procedure, it is possible to obtain repeated rapid measurements of plasma corticosterone concentrations from unanesthetized rats. Such a procedure reveals the existence of rapid corticosterone pulses with a duration of less than 60 s and amplitudes as great as 250 ng/ml. Several procedures were employed to determine that the pulses were not simply artifacts of the measurement and sampling methods. The existence of such rapid pulses provides for a duality of glucocorticoid function consisting of a rapid dynamic response capable of functioning simultaneously with, but independently of a slower long term regulatory response.

Effects of adrenocortical stress responses and metabolic functions during and after long-term administration of dexamethasone to adult Evans-Long rats.

During the last 75 days of a 130-day period of daily ip. administration of dexamethasone (DEX) sodium phosphate to adult female Evans-Long rats, mean body weight stabilized 20% below that of the controls, returning to the comparison-control level by the 64th day after the end of DEX treatment. Throughout the experiment, all animals received Purina Laboratory Chow, tap water, and a 0.7 M NaCl solution ad libitum. With DEX dosage, daily total fluid intake means determined weekly were consistently greater than the control values. There were 11 instances of increased saline intake also accompanied by significant increases in daily total fluid intake, but these did not establish salt dependency. Plasma corticosterone levels during DEX treatment were decreased significantly, but the DEX group was still responsive to stress; a significant within-subjects correlation, seen only in this group, between low- and high-stress corticosterone levels suggests that DEX selectively suppressed stress-release factors. Mean corticosterone levels of the DEX group sampled under conditions of increased stress did not exceed those for low-stress sampling of the controls. Following a recovery period after termination of DEX dosage, corticosterone levels were the same for both groups sampled under similar stress conditions and were not correlated with stress levels or with adrenal weights in either group.

Correlation between plasma thyroxine levels and corticosterone-binding activity in intact, ovariectomized, and ovariectomized estrogen-treated rats.

Plasma levels of total thyroxine (T4) and corticosteroid-binding activity (CBA) were determined in intact, ovariectomized, or ovariectomized, estrogen-treated rats during treatment with propylthiouracil (PTU) and following recovery from PTU. Propylthiouracil treatment reduced the mean plasma T4 concentration to 9 ng/ml and the mean plasma CBA to 39% of normal, while following recovery from PTU, the mean values for plasma T4 and CBA were 56 ng/ml and 108%, respectively. There was a strong (r equals plus +0.89) relationship between plasma levels of T4 and CBA as determined by linear regression analysis. Ovariectomy had no effect on either plasma T4 or CBA in euthyroid animals but significantly decreased CBA in PTU-treated, hypothyroid animals. The results indicate a robust influence of thyroid activity on plasma CBA and suggest a possible interaction between the thyroid and ovary in control of CBA.

Comparison of plasma corticosterone- and progesterone-binding activity in rat and human.

Corticosterone-and progesterone-binding activity were measured by saturation analysis, with dextran-charcoal separation, in plasma obtained from male and female rats, and a normal male and female human. In plasma from normal male and female rats, progesterone was much less effective than corticosterone in displacing 3H-corticosterone from plasma protein binding sites although the parallelism of the displacement curves indicated competition for the same binding sites. In plasma from the normal male human, corticosterone and progesterone were equally effective in displacing 3H-corticosterone. However, 3H-progesterone showed no apparent binding to either rat or human plasma proteins, suggesting that dextran-charcoal effectively removed progesterone from transcortin binding sites at 4 degrees C. This observation was confirmed by multiple equilibrium dialysis. In dialysis, 3H-corticosterone and 3H-progesterone were bound equally by human plasma, but rat plasma bound 3H-corticosterone to a much greater extent than it did 3H-progesterone. These data indicate that, in contrast to human plasma, rat plasma has much greater affinity for corticosterone than for progesterone.

Rapid pulsatile corticosterone response in unanesthetized individual rats.

Plasma corticosterone concentrations were determined by radioimmunoassay of blood samples obtained rapidly and repeatedly from individual unanesthetized rats at time intervals of approximately 10 seconds. Results confirm that corticosterone release is pulsatile, as has been reported previously, but with a much faster time course and a pulse frequency close to one pulse per minute. Such a release pattern is consistent with and required by the theory that there are rate sensitive hormone receptors. Failure of others to observe such a rapid response is presumably attributable to their use of much longer intervals between samples or of sampling procedures and techniques that obliterate any variation from a preconceived smooth function.

A general procedure for estimation of corticosteroid response in individual rats.

A procedure is presented whereby microliter volumes of plasma, obtained rapidly and repeatedly from the tail vein of unanesthetized rats, can be analyzed for corticosterone. Preliminary results suggest that (1) basal levels are considerably lower and (2) the latency to corticosteroid stress response is shorter than previously reported.

Long-term effects of adrenal and ovarian ablation on the regulation of energy exchange in the female rat.

Body weights of female rats in six postsurgical groups were observed over 120 days. Ovariectomy increased body weight as compared with controls, whereas adrenalectomy decreased it. Weights of animals that were both ovariectomized and adrenalectomized were intermediate between those of controls and adrenalectomized groups. The body weights of adrenalectomized rats that were not salt dependent resembled those of animals that had not undergone adrenal surgery. Plasma levels of corticosterone and progesterone were determined by radioimmunoassay. Adrenalectomy that resulted in salt dependency, whether or not in conjunction with ovariectomy, markedly decreased corticosterone levels. Ovariectomy alone or in conjunction with adrenalectomy decreased progesterone levels. The increased body weight of the group that was both ovariectomized and adrenalectomized over the group that was only adrenalectomized suggests that the decreased body weight generally observed for adrenalectomized animals may relate to mechanisms of voluntary regulation rather than frank debilitation.

Thiosemicarbazide injection followed by electric shock increases resistance to stress in rats.

Adult rats that had been raised with a minimum of stimulation were injected with thiosemicarbazide, a drug that lowers y-aminobutyric acid concentrations. Fifteen minutes later the animals were given 30 mild electric shocks over a half-hour period. Two. weeks later they were tested for their resistance to gastric ulceration induced by immobilization. The experimental animals showed a much greater resistance to stress than did the appropriate control groups. A replication confirmed the results of the first study.