El hipotálamo es la glándula coordinadora de todo el sistema. La hipófisis, junto con el hipotálamo, forma el eje hipotálamo-hipofisario, que constituye el. envejecer en el eje hipotálamo-pituitaria-adrenal (HPA) son contradictorios. Objetivo: este estudio examina la variación diurna de los niveles de cortisol salival. sistema endocrino. fisiología de la hipófisis. hormonas del crecimiento página de tema ii: fisiología de la hipófisis. hormonas del crecimiento hormonas.
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Paula Maria da Cruz, M. Cardiac surgery with cardiopulmonary bypass CPB is related to euthyroid disease or hypothalamic-pituitary-thyroid system depression. Abnormal hemodynamic tiroidel induced by CPB is responsible for several endocrine-metabolic changes, triggering complex systemic inflammatory response. This study aimed at evaluating triiodothyronine T 3tetraiodothyronine T 4 and thyrotrophin TSH behavior in infants submitted to cardiac surgery with CPB.
Participated in this study 15 infants. M 1 – after anesthetic induction; M 2 – at surgery completion; M 3 – six hours after surgery hipotaalmo M 4 – 24 hours after M 1.
To complete this study the following parameters were evaluated: The patients’ means aged, weigh, height and body surface were 3. Lowest T 3 and T 4 values were coincident with highest Ht and Hb values, discarding hemodilution effects.
Highest serum TSH concentrations have shown a possible hypothalamic-pituitary-thyroid system reaction to hypothermia and of massive iodine absorption topic use of antiseptic solutions. There have been changes in serum T 3T 4 and TSH concentrations in infants submitted to cardiac surgery with cardiopulmonary bypass. Fueron estudiados 15 lactantes. Abnormal hemodynamic status induced by CPB is responsible for several endocrine-metabolic changes, triggering complex systemic inflammatory response 1.
Euthyroid disease, evidenced by transient thyroidal hormones peripheral metabolism unbalance, is interpreted as an organic defense mechanism aiming at decreasing baseline metabolism, but it may also mean poor prognosis In the lab it is manifested in two ways 5: This phenomenon is caused by lower desiodinase type 1 – 5 activity, which is the enzyme normally responsible for generating T 3 as from T 4 and for the production of diiodothyronines as from T 3 r inactive metabolite.
As result, T 3 is not satisfactorily produced while serum T 3 r rates are increased.
Eje Hipotalamo – Hipofisis – Tiroides by Liliana Contreras on Prezi
The situation is further worsened by further alternative metabolic pathway action through desiodinase type 1 – 5, which generates T 3 r but not T 3 as from T 4.
Hipodisario T 3 r rates are then increased by higher production and inadequate clearance. In this case, serum T 3 r concentrations are virtually not changed because type 1 – 5 desiodinase alternative pathway does not find enough substrate, which is T 4.
Euthyroid disease has already been documented in adults submitted to cardiac surgery with CPB; however pediatric patients have uncertain behavior due to immaturity 6. Exclusion criteria were children with congenital thyroidal metabolism disorders, hypothalamic-pituitary-thyroid system disorders, having received iodine contrast cardiac catheterization or with tiroideeo with thyroid dysfunction.
M 1 – after anesthetic induction; M 2 – at surgery completion; M 3 – 6 hours after surgery completion; M 4 – 24 hours after M 1. The following parameters were also evaluated: General anesthesia was induced with fentanyl, midazolam and pancuronium 7. T 3 and T 4 were dosed by the radioimmunoassay method and TSH was dosed by the immunoradiometric method.
Highest T 3 although slightly below normal reference values and T 4 means were obtained in M 1. Lowest T 3 and T 4 means were found in M 4. Numeric results are shown in table Hipofsariowhile hipofiszrio concentrations along time are shown in figure 12 and 3. Highest Ht and Hb concentrations were found in M 4. According to hormonal means obtained, it is possible to consider that early on M 1 there were already lab aspects of “Low T 3 Syndrome”, and several factors may have contributed for such: Hypercatabolic state, when present, is the result of excessive catecholamines production and not of thyroid hormones hyperactivity.
Thyroid hormonal activity depression is also common 12. Adults submitted to hour food suppression have developed “Euthyroid Sick Syndrome”, characterized by lower tissue T 4 conversion with progressive generation of T 3 r. Oral glucose normalizes serum T 3 13. Highest serum TSH concentrations although within normal limits were obtained in M 2suggesting that there has been more pituitary stimulation at cardiac surgery completion.
However, lab aspects of “Low T hiopfisario Syndrome” still remained. Topic application of iodinated products anti-germ and iodine tincture in children results in massive iodine absorption by the skin not necessarily with previous integrity disruption.
Contamination is proven by increased serum and urinary concentrations of this ion Primary transient hypothyroidism is configured and characterized by significant plasma TSH increase together with decrease in T 3T 4 and their free fractions Another aspect to be considered is the interference of drugs. Steroids, used to attenuate CPB-induced inflammatory response, directly reach three metabolic sites: Dopamine depresses pituitary activity leading to lower TSH production even after stimulation with exogenous TRH thyrotrophin release factorwith lab installation of secondary or transient pituitary hypothyroidism Heparin releases lipases and, as a consequence, triglycerides hydrolysis into non-esterified free fatty acids, impairing the binding of hormones to plasma proteins Heparin also prevents the binding of hormones to specific protein sites.
Increased blood fatty-acids due to its use, however, seems to be of little relevance in neonate and infant cardiac surgeries Increased free hormones T 3 F and T 4 F during CPB 21 have been attributed to the administration of sodium bicarbonate which, like heparin, changes the biochemical affinity of hormones to circulating proteins.
Possible prolonged metabolic acidosis may also affect intracellular conversion of T 4 into T 3 Systemic inflammatory response, undesirable event inherent to CPB, interferes with thyroid hormones secretion through the release of immune system chemical mediators. The presence of cytokines during pediatric surgeries has been reviewed by Saatvedt et al.
IL-6 and tumor necrosis factor, released during CPB-induced hypoperfusion, possibly due to intestinal bacterial translocation, decrease T 3 generation as from T 4 and decrease serum TSH 24,25 depressing effect on pituitary. Non-pulsatile blood flow, directly responsible for transient anterior pituitary secreting hypofunction, also affects the hypothalamic-pituitary-thyroid system, decreasing the amount of serum cortisol. We have considered a possible influence of inadvertent thyroid hormones administration in the perfusate through blood transfusion, but this was considered irrelevant due to hemodilution 29,30 half-lives of T 3T 4 and TSH present in one red-cell concentrate unit are respectively: Proteins scavenging observed in adult surgeries with the use of Cell Saverhowever, has been substantial and also seems to explain the increase in T 4 F after CPB in pediatric surgeries Hypothermia activates the hypothalamic-pituitary-thyroid system promoting sympathetic nervous system hyper-reactivity with the release of catecholamines in the plasma Experimental studies in rats have shown increased plasma TSH 30 minutes after exposure to cold, due to intensive pituitary stimulation with higher TRH production TRH secretion in these conditions is independent of the amount of TRH previously present in the hypothalamus during normothermal situations 34, Fundamental thyroid metabolic changes in neonates are based on abrupt fetal exposure to the extra-uterine environment, with sudden circulating TSH increase three hours after birth.
Chronic exposure to cold is also related to increased T 3 and T 4 12, A comparative study with children 1. The interpretation of M 2 results shows lower T 3 and T 4 rates together with increased TSH, and it should be highlighted that the effects of acute contamination with iodine and of hypothermia were possibly preponderant.
This way, in this study, it was observed that neuraxis was not depressed, suggesting that it has actively responded to these factors.
Progressive T 3 and T 4 decrease would not be related to hemodilution effects, since highest Ht and Hb means were found in M 4. However, even in these two situations, there were lab evidences of “Low T 3 Syndrome”. In our study, cardiac surgery with CPB for congenital heart disease correction in infants has promoted significant changes in T 3T 4 and TSH behavior during the studied period.
This way, there are several etiologies promoting thyroid metabolic changes during pediatric cardiac surgeries. The major cause of intraoperative primary hypothyroidism, surely promoted by acute and massive iodine absorption by the skin as a consequence of the use of anti-septics 16,37could have been totally abolished since there are other non-iodinated compounds that are also effective.
Cases of hipotzlamo in a short period of time may mean further and even more hipotxlamo contamination. Excess iodine in the body may lead to prolonged thyroid hypofunction state called Wolff-Chalkoff effect or thyroid peroxidase blocka long time described in adults. This means that during this period, excessive iodine is not incorporated to thyroglobulin molecule present in glandular parenchymal colloidal substance.
This organic phenomenon prevents the disproportional production of circulating T 3 and T 4 and consequent systemic metabolic unbalance hyperthyroidism. Effects of this unbalance in infants are not known, but it is known that it persists while all uptaken and retained iodine in the thyroid is not excreted.
Initial result is decreased glandular T 3 and T 4 production with simultaneous serum TSH increase 13, Some studies have shown that hypothermia is an independent factor promoting, per seexpressive pituitary response with increased circulating TSH In this case, this is an additional effect similar to iodine contamination.
There are however other agents during pediatric cardiac surgeries with CPB, which may simultaneously promote transient secondary hypothyroidism that is, pituitary response depression 17,29, Among them, few may be abolished or at least attenuated, since they are inherent to intraoperative and anesthetic techniques, such as the use of drugs as steroids, dopamine, heparin, furosemide, sodium bicarbonate, non-pulsatile blood flow and hemodilution 1,8,12,14,19,22,24, One has to consider, however, that in normal physiological conditions, pituitary responds to massive iodine absorption with increased TSH productionprovided there is no situation maintaining it hypofunctioning, such as those intervening during the perioperative period.
The conclusion, then, is that during infant cardiac surgery, thyroid function is the result of all effects acting sometimes on the direct production of hormones by sje gland and increasing circulating TSH primary hypothyroidismsometimes on the hypothalamic-pituitary-thyroid axis decreasing TSH secondary hypothyroidism 20and sometimes on peripheral thyroid hormones metabolism.
These manifestations, if transient, hipotalzmo the presence of euthyroid disease 13,31characterized by reversible but sometimes prolonged thyroid function disorders with extremely relevant postoperative effects In this study it was not possible to investigate the real magnitude of pituitary response to exogenous iodine contamination, although increased serum TSH has prevailed. Ann Thorac Surg, ; J Am Coll Cardiol, ; Ann Intern Med, ; J Thorac Cardiovasc Surg, ; Mitchell IM – Liver function after cardiopulmonary bypass in children.
Bartalena L – Recent achievements in studies on thyroid hormone-binding proteins. hipofisxrio
Smerdely P, Lim A, Boyages SC et al – Topical iodine-containing antiseptics and neonatal hypothyroidism in very-low-birthweight infants. Crit Care Med, ; Mitchell IM – Thyroid function after cardiopulmonary bypass in neonates. Changes in plasma-free thyroid hormones during cardiopulmonary bypass.
Tahirovic HF – Thyroid hormones changes in infants and children with metabolic acidosis. J Endocrinol Invest, ; Saatvedt K, Lindberg H – Depressed thyroid function following paediatric cardiopulmonary bypass: Scand J Thorac Cardiovasc Surg, ; Rev Bras Anestesiol, ; J Clin Endocrinol Metab, ; III – Response of anterior pituitary gland to thyrotropin-releasing hormone. Reinhardt W, Mocker V, Jockenhovel F et al – Influence of coronary artery bypass surgery on thyroid hormone parameters.