Thyrotropin and prolactin response to intraspinal TRH administration in man

The effect of intraspinal (i.s.) TRH administration of Prolactin (Prl) and thyrotropin stimulating hormone (TSH) serum levels was studied in order to verify the existence of a ventricular route in man for releasing factor delivery to the anterior pituitary, which has been previously reported in rats. Ten young male subjects were given 200 microgram thyrotropin releasing hormone (TRH) i.s. injections and Prl and TSH were measured by radioimmunoassay (RIA) before and at various times after TRH administration. In the same subjects, an i.v. TRH test was also performed. After i.s. TRH, a prompt Prl increase (peak values at 10-30 min and return to baseline within 150 min) and a delayed increase (3-5 h following TRH injection) were observed in 7 and 5 subjects respectively, while an early elevation in serum TSH occurred in 6 subjects and a late one in other 6. In two subjects, a biphasic response of both tropins was present. Prl and TSH response to i.v. TRH was within the normal range in all cases; no late rise of the 2 hormones was observed. A kinetic experiment with 125I-TRH was also carried out to elucidate the mode of i.s. vs i.v. TRH action. These results confirm in man data reported in animals which suggest that TRH can be transported from the cerebrospinal fluid (CSF) to the portal system and the hypophysis.

Growth hormone levels in diabetes. Correlation with the clinical control of the disease

We carried out contemporaneous daytime blood sugar and growth hormone (HGH) determinations in eight juvenile and six middle-aged diabetics under both poor and good metabolic control. A continuous blood sampling technic was used. The following results were obtained: 1. HGH values in poorly controlled diabetics were higher and more fluctuating than in normals of a corresponding age. 2. After good control was reached, a significant HGH decrease was observed in all patients but one. In this condition HGH levels were normalized in middle-aged diabetics but not in juvenile ones. In the latter group HGH values, even if decreased, were persistently higher than in controls of the same age. 3. No difference was observed between newly diagnosed diabetics and patients known to have had diabetes for some years. Our data support the suggestion that HGH abnormalities in diabetes are a consequence of the metabolic disturbance.

Effect of dexamethasone on thyroid hormone response to TSH

The effect of short-term dexamethasone administration (8 mg daily for 3 days) on thyroid hormone response to exogenous TSH (bovine TSH, 5 IU i.m.) was studied in 16 euthyroid volunteers. Serum T3 and T4 concentrations were measured by radio-immunoassay prior to and 2, 6, 12, 24, and 49 hr after bTSH injection, both under basal conditions and during dexamethasone treatment. In all subjects bTSH administration raised both T3 and T4 concentrations significantly. Dexamethasone treatment induced a slight depression of endogenous TSH (m +/- SEM = 2.0 +/- 0.4 versus 1.6 +/- 0.3 muU/ml) and T4 (6.8 +/- 0.4 versus 6.1 +/- 0.2 mug/100 ml) basal values and a significant decrease in T3 value (1.16 +/- 0.09 versus 0.64 +/- 0.06 ng/ml, p = 0.005). The mean increment of both T3 and T4 after bTSH injection was percentually unchanged during dexamethasone treatment but, due to lowered basal value, T3 levels at each time interval after TSH + dexamethasone were significantly lower than the corresponding values observed after TSH alone. The present data show that high dexamethasone doses decrease T3 serum levels significantly without inhibiting T3 response to TSH stimulation. Only a slight lowering was observed in T4 levels.

The effect of short-term triiodothyronine administration on thyroxine response to exogenous TSH in man

In order to examine whether thyroid hormone concentration interfere with the thyroid gland responsivity to TSH, paired studies on the effect of short-term T3 treatment on T4 response to exogenous TSH ( 5 I.U. i.m.) were carried out in 10 euthyroid volunteers. During T3 administration ( 120 mcg/day for 4 days starting 48 hr before TSH injection) a significant decrease in T4 concentrations was observed both prior to and after TSH, with an inhibition of the T4 response ranging from 36-77% as calculated from the area under the response curve. The present data are in agreement with the existence of a "short-loop" thyroid-thyroid regulatory mechanism in man. In fact, the decreased percent rise of T4 after TSH suggests an inhibitory effect of T4 release following TSH, even though a modification of T4 kinetic parameters during T3 administration may account for a portion of the lowering of T4 blood concentrations.

Growth hormone kinetics in diabetic patients

Several reports have shown that average plasma GH concentrations in insulin-treated and in juvenile diabetics are elevated in respect to normal values: these findings have been alternatively attributed to an increased pituitary GH secretion or to a lower GH catabolism induced by the disease. To reinvestigate the problem we studied GH kinetics in twenty-four diabetics using 125-I-GH. The patients were all normal in body weight and their fasting blood sugar did not exceed 190 mg. per 100 ml.; fourteen normal subjects were included as a control group. After single injection of the tracer, the plasma disappearance curve of labeled hormone was obtained. Starting from this curve, metabolic clearance rate (MCR), fractional catabolic rate (FCR), initial distribution volume (IDV), and total distribution volume (TDV) were computed; MCR and plasma concentration of endogenous GH in plasma samples were used to estimate the amount of hormone irreversibly lost during the experiment (IHL240). The major points that result from the comparison of the values obtained in diabetic patients with those in the normal group are: MCR values in diabetics do not differ from those found in normals (63.6 plus or minus 19.6 and 64.6 plus or minus 24.3 ml./min./m.-2 respectively). The higher plasma concentrations of endogenous GH in diabetics together with a normal MCR, yield hormone loss values (IHL240) significantly larger than normal (46.4 plus or minus 29.5 mug/240 min. as compared to 23.7 plus or minus 24.5) thus indicating that an increased GH secretion is present in diabetics. TDV, fairly constant in normals, (5.8 plus or minus 0.9 L./ml-2) tends to decrease in diagetic patients as the disease progesses; in fact the values of TDV are significantly reduced (P less than 0.005) in long-term diabetics (greater than 10 yrs. of disease) while TDV of short-term diabetics (less than 10 yrs.) does not differ from the normal value (4.6 plus or minus 1.16 L./m.-2 and 5.8 plus or minus 0.9 L./m.-2, respectively).

Spontaneous fluctuations of human placental lactogen during normal pregnancy

Six women in the 3rd trimester of normal pregnancy had measurements of circulating placental lactogen (hPL) levels using a continuous blood sampling technique for 10-15 h. In addition, in 3 pregnant women hPL was assayed at 10-min intervals for 60-90 min. Both these procedures showed that hPL serum levels fluctuate irregularly during normal pregnancy. The magnitude and frequency of these fluctuations make the significance of a single hPL determination less reliable as a test of placental function.

Triiodothyronine and thyrotropin-releasing hormone interaction on TSH release in man

In order to study thyrotropin releasing hormone (TRH)-thyroid hormone interaction, we examined thyrotropin (TSH) behaviour after synthetic TRH administration in 24 euthyroid subjects, 3 patients with primary hypothyroidism and 10 hyper thyroids. 8 normal subjects were studied before and after triiodothyronine (T₃) treatment with increasíng TRH dosage. Our results suggest that (1) TRH-thyroid hormone interaction is dose-related: this means that TSH response to TRH depends on both thyroid hormone and TRH concentration; (2) T₃-TRH interaction on TSH release is only roughly quantitative since it is suggested that other extrathyroidal factors interfere with this mechanism controlling TSH secretion.