EFFECT OF ALTERED THYROID FUNCTION UPON ADRENOCORTICAL ACTH AND METHOPYRAPONE (SU-4885) RESPONSIVENESS IN MAN

Neuroendocrine evidence for an association between hypothyroidism, reduced central 5-HT activity and depression

OBJECTIVE

The incidence of depression in those with hypothyroidism is increased compared to healthy populations, though the mechanism for this is unclear. We tested the hypothesis that central 5-HT activity is reduced in hypothyroidism, and that this subsequently lowers the threshold for developing depression.

PATIENTS

Twenty subjects entered the study: 10 drug free hypothyroid patients and 10 age, sex, weight and menstrual cycle matched controls.

MEASUREMENTS

Patients were diagnosed as being depressed using DSM-IIIR criteria and rated using the Hamilton Rating Scale for Depression (HAM-D) and Beck Depression Inventory (BDI). Cortisol and prolactin responses to dexfenfluramine, a centrally acting 5-HT releasing agent, were used as an index of central 5-HT responsivity.

RESULTS

Both cortisol and PRL responses were reduced in the hypothyroid group relative to the controls. Peak cortisol responses were inversely correlated to TSH levels. Four of the 10 patients were clinically depressed. Depressed patients had higher TSH levels than their non-depressed counterparts, and TSH levels were positively correlated with HAM-D and BDI scores.

CONCLUSIONS

These findings support animal work suggesting that hypothyroidism reduces central 5-HT activity. They also suggest a threshold effect in that higher TSH levels predicted both lower 5-HT mediated endocrine responses and the presence of clinical depression.

Circadian and seasonal changes in ACTH-induced effects in healthy young men

The effects of the ACTH 1-17 analogue (100 micrograms i.m.) as a function both of time of day (7.00, 14.00 and 21.00 h) and season (winter versus summer) were determined on a set of physiological variables: urinary 17-hydroxycorticosteroids, oral temperature, grip strength (right and left hands), peak expiratory flow and self - rated fatigue. Six young healthy males took part in the study in January-February 1980 and June-July 1981. They were synchronized with a diurnal activity from 7.00 to midnight and a nocturnal rest. Urine was collected every 3 to 4 hours, at fixed clock hours over 72 h (winter) and 48 h (summer). There was a one week interval between each ACTH test or placebo control. Variables were measured according to the same schedule. 24 h urinary 17-OHCS excretion was maximum for ACTH injected at 7.00 in winter and 14.00 in summer, and the minimum occurred after ACTH given at 21.00. The highest peak of urinary 17-OHCS was found after ACTH at 7.00 both in winter and in summer. It is likely that the maximal stimulation of glucocorticoid secretion occurs when ACTH is administered around the beginning of the activity span. Both in winter and summer the injection of ACTH at 7.00 was followed by the greatest decrease in self-rated fatigue (24 h mean) and the largest increase (24 h mean) both in grip strength and peak expiratory flow (bronchial patency) in comparison with other times of ACTH administration (14.00 and 21.00 h).

New aspects of human chronopharmacology

Regular and thus predictable changes in biologic susceptibility and response to a large variety of physical as well as chemical agents can now be viewed as a rather common phenomenon. Chronopharmacology involves both the investigation of drug effects as a function of biologic timing and the investigation of drug effects upon rhythm characteristics. Illustrative examples of circadian chronopharmacolgy in man are discussed, keeping in mind that the objective demonstration of chronopharmacologic facts needs the use of an appropriate methodology. Circadian changes in the effects of various chemical agents have been documented: histamine, sodium salicylate, acetylcholine, halothane, prostaglandine F, reserpine, cyproheptadine, ethanol, insulin, chlorothiazide, oxymetholone, orciprenalin and SCH 1000 (bronchodilators), indomethacin, ACTH, cortisol and various synthetic corticosteroids. (three new concepts have to be considered: a. The Chronokinetic of a Drug. This term includes both rhythmic changes in the drug vioavailability, pharmacokinetic and its excretion. b. The Chronesthesy of a Biosystem to a Drug. i.e. circadian changes in the susceptibility of any biosystem to a drug. c. The Chronergy of a Drug, taking into consideration its chronokinetic and the chronesthesies of the involved organismic biosystems. Chronopharmacology is useful to solve problems of drug optimization, i.e. to enhance the desired effeciency or to reduce its undesired effects. In the human organism (among other animal species) the metabolic fate of a pharmacologic agent (as well as that of a nutrient) is not constant as a function of time. Thus, the chronobiologic approach of pharmacologic phenomena involves a lesser risk of errors and/or false information than the conventional homeostatic approach.