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L Huffman

Publications and source records attributed to L Huffman.

8 recordsLinked to original sources
PubMed1990

Helodermin, but not cholecystokinin, somatostatin, or thyrotropin releasing hormone, acutely increases thyroid blood flow in the rat.

In the present study, we investigated whether peptides located within the thyroid gland, but not directly found in nerve fibers associated with blood vessels, might influence thyroid blood flow. Specifically, we evaluated the effects of helodermin, cholecystokinin (CCK), somatostatin (SRIF) and thyrotropin releasing hormone (TRH) given systemically on thyroid blood flow and circulating thyroid hormone levels. Blood flows in the thyroid and six other organs were measured in male rats using 141Ce-labeled microspheres. Circulating thyrotropin (TSH) and thyroid hormone levels were monitored by RIA. Helodermin (10(-10) mol/100 g BW, i.v. over 4 min) markedly elevated thyroid blood flow (52 +/- 6 vs. 10 +/- 2 ml/min.g in vehicle-infused rats; n = 5). Blood flows to the salivary gland, pancreas, lacrimal gland and stomach (but not adrenal and kidney) were also increased during helodermin infusions. CCK, SRIF, and TRH were without effect on blood flows to the thyroid and other organs even though these peptides were tested at higher molar doses than helodermin. Helodermin, CCK, or SRIF did not affect thyroid hormone or plasma calcium levels. As expected however, plasma TSH and T3 levels were increased at 20 min and 2 h, respectively, following TRH infusions. Since helodermin shares sequence homology with VIP, we next compared the relative effects of these two peptides on thyroid and other organ blood flows. VIP (10(-11) mol/100 g BW, i.v.) was more potent in increasing blood flows to the thyroid, salivary gland, and pancreas than an equimolar dose of helodermin. This study shows that while helodermin, like VIP, has the ability to increase thyroid and other organ blood flows, it appears to be a less potent vasodilator.

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PubMed1988

Early development of the thyroid axis in the Brattleboro rat.

Plasma concentrations of thyrotrophin (TSH), thyroxine (T4), and triiodothyronine (T3), and pituitary TSH concentrations were determined at weekly intervals during the first 42 days following birth in Brattleboro homozygous (DI), Brattleboro heterozygous (HZ), and Long-Evans (LE) rats. Offspring from matings of Brattleboro rats were divided into DI and HZ animal subgroups on the basis of hypothalamic vasopressin content. In control LE rats, circulating levels of TSH, T4, and T3, and pituitary TSH concentrations increased during the early postnatal period to reach relatively stable levels between 28 and 42 days of age. In DI and HZ rats, the thyroid axis developed in parallel to that of LE rats during initial postnatal weeks. However, by 42 days of age, pituitary TSH concentrations were clearly elevated in Brattleboro rats relative to levels in age-matched LE animals. These data indicate that differences in thyroid axis function between Brattleboro and LE rats occur only after the attainment of a degree of maturity.

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PubMed1986

Neuropeptide control of thyroid blood flow and hormone secretion in the rat.

The effects of peptide HI (PHI), neuropeptide Y (NPY), and substance P (SP) on thyroid blood flow and hormone levels were studied in anesthetized rats. Regional blood flows were determined using radioactive microspheres. No change in heart rate or mean left ventricular pressure occurred during these neuropeptide infusions (0.625 micrograms iv over 2 min). PHI treatment resulted in a four-fold increase in thyroid blood flow. Blood flows to the pancreas and salivary gland also increased during PHI treatment. Infusions of NPY or SP did not significantly alter thyroid blood flow. However, SP decreased blood flow to the spleen and small intestine. These neuropeptides had no effect on blood flows to the adrenal, kidney, brain, heart, and adipose tissues. Following PHI, NPY, and SP infusions, plasma triiodothyronine and thyroxine levels were not different from values in saline-treated rats. This study demonstrates that PHI, like vasoactive intestinal peptide, is a potent thyroidal vasodilator at a dose that does not affect circulating thyroid hormone secretion.

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PubMed1986

Effects of vasoactive intestinal peptide on thyroid blood flow and circulating thyroid hormone levels in the rat.

The effects of vasoactive intestinal peptide (VIP) on thyroid blood flow and hormone levels were studied in rats. Tissue blood flow was determined from the distribution of radioactive microspheres after injection by cardiac puncture directly into the left ventricle of anesthetized rats. Initial results indicated that the systemic infusion of 6.25 micrograms VIP iv resulted in increased thyroid blood flow, but was also associated with hypotension, as measured by left ventricular pressure. In contrast, topical administration of VIP to the left of the thyroid increased blood flow to that lobe, but not to the right lobe, and produced no systemic cardiovascular effects. In a further set of experiments, graded doses of VIP were administered iv. Infusions of 6.25 and 0.625 micrograms VIP were associated with 2- to 3-fold increases in thyroid and pancreatic blood flows, but lower doses were ineffective. Blood flows to the adrenals, brain, small intestine, kidneys, and spleen were not altered by any dose of VIP. Mean left ventricular pressure was again reduced by the 6.25-micrograms dose of VIP, but was not affected by lower doses. The infusions of VIP had no effect on plasma TSH, T3, or T4 levels either 20 min or 2 h after treatment. These results suggest that thyroid blood flow is, in part, controlled by VIP and indicate that changes in thyroid blood flow can occur at doses of VIP that have no apparent effect on circulating thyroid hormone levels.

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PubMed1983

Carotid sinus baroreceptor activity in the nonhuman primate.

The carotid sinus of eight adult Macaca fascicularis monkeys was functionally isolated from the circulation and perfused with Krebs-Henseleit solution. The impulse activity in 65 carotid sinus baroreceptor fibers from the left carotid sinus nerve was studied during nonpulsatile perfusion and was compared with the impulse activity in 68 fibers from 10 adult mongrel dogs. Curves relating the discharge frequency to carotid sinus pressure were constructed. The baroreceptor fibers of the monkey had a significantly lower threshold, gain, pressure at the point of inflection, and plateau pressure than those of the dog. Hysteresis, as indicated by the separation of the stimulus-response curves obtained by increasing and then decreasing carotid sinus pressure, was observed. At any given pressure, the discharge frequency of baroreceptors was greater when carotid sinus pressure was increased than when it was decreased in both species. These results provide direct evidence that carotid sinus baroreceptors in the monkey are less sensitive to pressure changes than those in the dog.

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