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Biomedical subjects

M T Hays

Publications and source records attributed to M T Hays.

At least 55 records · Page 3Linked to original sources
PubMed1979

Kinetics of the human thyroid trap: effects of iodide, thyrotropin, and propylthiouracil.

Effects on the thyroidal pertechnetate trap of iodide, thyrotropin (TSH), and propylthiouracil (PTU), compared with duplicated control studies, were assessed in normal subjects using i.v. [Tc99m] pertechnetate, a multicrystal scintillation camera, and a compartmental model. Sodium iodide (1 g), administered orally on two occasions, 2 wk apart, caused an early drop in plasma clearance into the follicular cell (p less than 0.05), with later return to normal clearance 1 wk after the second NaI dose. In this later study, exit from the colloid was elevated (p less than 0.01). Plasma equivalent volume of the "colloid" compartment was reduced in both postiodine studies (p less than 0.05). Thyrotropin, 10 units intramuscularly, was followed by no significant changes in trap parameters at 2 hr. At 24 hr, plasma clearance had doubled (p less than 0.05), and the plasma equivalent "colloid" volume had tripled (p less than 0.01). Propylthiouracil was given as a single 1 g dose 1 hr before a trapping study followed by 200 mg PTU every 8 hr for 1 wk. The first dose resulted in apparent reduction in all of the rate constants for transport across the basal and apical thyroid follicular cell membranes; these rates returned toward control levels after 1 wk. The plasma equivalent "follicular cell" volume was reduced to 66% of controls levels (p less than 0.025) after 1 wk PTU. These effects must be taken into account in the interpretation of studies of the trap based on PTU pretreatment to inhibit organification.

Adult↗
PubMed1978

Kinetics of the human thyroid trap: a compartmental model.

Thyroidal pertechnetate was measured continuously in normal subjects for 40 min after i.v. injection, using a multicrystal camera. Digital counts (1-min increments) were read directly from the magnetic tape and summed for the thyroid area and for adjacent neck background. The net thyroidal data were used as the basis for development of a compartmental model of the thyroidal trap, using the SAAM program. Input to the trap in the model is plasma pertechnetate radioactivity, measured frequently during the study and fitted to a multiexponential equation. Best fit of the thyroid data was achieved with a model in which the trap is described by two compartments, a fast ("follicular cell") compartment and a slower ("colloid") compartment. Iodide blockade, administered either during the study or 1 hr before its initiation, rapidly blocked the trap at the point of input from plasma into the follicular cells. Iodide did not affect the other parameters of the model.

Adult↗
PubMed1977

Ultrastructural changes in dog thyroid follicular cells elicit by concanavalin A in vitro.

Dog thyroid follicular cells exposed to concanavalin A (Con A) in vitro showed changes in cell shape, induction of colloid droplets and alterations in the distribution of microvilli. Cells exposed to Con A plus suboptimal concentrations of TSH (thyroid stimulating hormone) showed pseudopods and their cytoplasm was virtually occupied with colloid droplets. This findings suggest that Con A potentiated pseudopod and colloid droplet formation induced by TSH.

Animals↗
PubMed1977

Pertechnetate distribution in man after intravenous infusion: a compartmental model.

Using a primed infusion technique, distribution of pertechnetate was monitored in normal volunteer subjects over an 8-hr period. Two groups of subjects were studied, during hours 0-4 (n = 8) and hours 4-8 (n = 7), respectively, of the infusion. At 6.5 hr a large dose of NaI (1000 mg) was administered intravenously to the second group. Plasma, salivary, and urinary radioactivities were assayed, and external counts were made of radioactivities over the neck, thigh, and right upper abdomen. A kinetic model was developed for pertechnetate based upon the distribution data, the iodide perturbation, and known physiology for pertechnetate and iodide. The model has three major subsystems: (1) the thyroid trap; (2) a whole-body distribution, containing plasma and two extravascular compartments; and (3) the gastrointestinal tract, including the salivary, stomach (including upper small intestine), and two lower intestinal compartments. One of the latter, which turns over very slowly, is believed to represent bowel wall. The large NaI dose markedly reduced transport into compartments of the thyroid trap, the saliva, and the stomach and small intestine. This study shows that, in most respects, pertechnetate is distributed qualitatively but not quantitatively like iodide but that, unlike iodide, large bowel distribution plays an important role, especially in long-term studies.

Adult↗
PubMed1976

Stability of radiothyroxine plasma disappearance curve despite catharsis and unblocked thyroidal uptake of radioiodide.

Plasma radioactivity was measured over 21 days after an intravenous injection of 50 muCi of 125I-T4 in eight normal men. No thyroid-blocking medication was given. Four subjects (castor oil group) received 30 ml of castor oil on each of Days 13, 14, and 15, while the other four subjects (control group) were studied without medication. After A 5-day equilibration period, plasma 125I-T4 was measured on Days 5-13 in order to calculate the disappearance curve for each subject and to derive the mean for each experimental group. The curves were then extrapolated to Day 21. Measured radioactivity did not depart significantly from the extrapolated line, either during the castor oil period (Days 14, 15, and 16) or during the recovery period (Days 17, 19, and 21). The castor oil, therefore, had no observable effect on the clearance of plasma radioactivity. None of the subjects had a late increase in plasma radioactivity to suggest recirculation of radioiodide or buildup of iodoproteins. In normal subjects, radiothyroxine plasma levels up to 21 days are not significantly affected by short-term catharsis or by failure to block thyroidal radioiodide uptake.

Adult↗
PubMed1975

Alterations in cyclic necleotides in dogs after triiodothyronine.

The effects of triiodothyronine (T3) on plasma and tissue levels (liver, adipose tissue, muscle) of adenosine 3',5'-monophosphate (cyclic GMP) were determined in Mongrel dogs. Plasma cyclic AMP increased to a mean plateau value 165% greater than control values in response to a single intravenous injection of T3 (100-200 mug/kg body weight). This treatment resulted in no increase in plasma cyclic GMP. In liver, cyclic AMP concentration decreased 54%, while cyclic GMP increased 137%. Adipose tissue cyclic AMP levels decreased in control animals during the experimental procedure. On the other hand, animals given T3 had stable or (in one case) increasing adipose tissue cyclic AMP levels. Hence, T3, actually maintained higher levels than that expected, in comparison to the control. Cyclic GMP levels in adipose tissue were not affected by T3. Cyclic AMP and cyclic GMP were unchanged in muscle. In all cases, a time lag occurred (30-45 min) between administration of T3 and subsequent alterations in cyclic nucleotide levels. It was concluded that T3 is capable of altering concentrations of cyclic AMP and cyclic GMP in vivo and that cyclic AMP and cyclic GMP patterns of response are completely different. In liver, a converse relation of the two nucleotides is present. These findings are compatible with the hypothesis that some of T3's action may be explained by its effects upon either cyclic AMP or cyclic GMP.

Adipose Tissue↗
PubMed1969

Effect of epinephrine on the peripheral metabolism of thyroxine.

10 normal young men received repository epinephrine repeatedly for 4 days during the course of a radiothyroxine (radio-T4) disappearance curve. During epinephrine administration, serum radio-T4 disappearance rate (k) slowed abruptly, fecal clearance decreased, urinary clearance was initially unchanged but later decreased slightly, volume of thyroxine distribution decreased, and external radioactivity over the liver remained unchanged. Beginning on day 2 of epinephrine and persisting at least 1 day after epinephrine was discontinued, serum thyroxine-binding globulin (TBG) maximal binding capacity increased, thyroxine-binding prealbumin (TBPA) maximal binding capacity decreased, and free T4 iodine decreased. Stable serum T4 iodine decreased during the experiment. Three indexes, namely the free T4 iodine, the reciprocal of TBG capacity, and the urinary radio-T4 "clearance" changed in parallel, suggesting that the increase in TBG capacity was responsible for a delayed decrease in radio-T4 metabolism. However, these changes were temporally dissociated from the decrease in k, which began and ended abruptly with initiation or discontinuing of epinephrine administration. This dissociation is unexplained, but may be caused by alterations in T4 binding in tissue sites.

Epinephrine↗