Background: Kisspeptin and its cognate receptor GPR54 are the central driving forces in the hypothalamus-pituitary-gonadal axis essential for sexual maturation and reproduction. Kisspeptin/GPR54 signalling stimulates gonadotropin-releasing hormone (GnRH) neurones and induces pulsatile GnRH release. The molecular signalling pathway by which kisspeptin stimulates GnRH neurones is currently under investigation. Methods: Primary GnRH neurones were isolated from young adult rats and loaded with the calcium indicator Fura Red. Cytosolic calcium was measured while the cells were stimulated with kisspeptin. Results: GnRH neurones show a maintained increase of cytosolic calcium upon stimulation with 100 nM kisspeptin-10. The calcium elevation was inhibited 30% by 1 µM tetrodotoxin, a voltage-gated sodium channel blocker, and 76% by 30 µM SKF96365, an inhibitor of receptor-mediated calcium entry. Furthermore, removal of extracellular calcium completely abolished the kisspeptin-induced calcium elevation. Conclusion: Our results suggest that the major part of the kisspeptin-evoked calcium signal is generated by an action potential-independent calcium influx, possibly through channels of the classical transient receptor potential type, with an additional influx through voltage-gated calcium channels activated by sodium action potentials.

T4-, T3- and reverse-T3 concentrations were measured in the sera of 365 subjects beyond the age of 65 in order to evaluate if the decrease of serum T3 frequently observed in old age can be attributed to old age per se or to concomitant nonthyroidal disease. The results obtained from a carefully selected healthy group of elderly people show that 1) total and free T3 levels are lower in senescence but well within the range for euthyroidism in younger healty controls;2) the decrease of serum T3 is more pronounced and occurs earlier in healthy old males than in females, so that for subjects over the age of 75, the upper limit for euthyroidism has to be adjusted by 10% in women and by 20% in men; and 3) there is no low T3 syndrome characterized by decreased serum T3 and increased serum reverse T3, solely due to old age. Turnover kinetics have shown the daily production of T4 and T3 in old age to decrease by 20 micrograms and 10 micrograms, respectively, and an increased T3 metabolic clearance not to account for the reduction of serum T3 concentrations. Combined stimulation tests with TSH and TRH showed that the functional reserve of the thyroid gland to produce T3 is maintained in old age. The first step in the sequence of events may be seen in an impairment of TSH secretion leading to an adaptation of the amount of thyroid hormones to a reduced mass of metabolically active body tissue in old age.

Free Triiodothyronine (T3)-and Thyroxine (T4) Serum Levels in Old Age 239 Due to the ubiquitous distribution of adipose tissue and the substantial insulin degrading activity observed, it would appear that this tissue may play an important role in insulin turnover in the body. References

Zusammenfassung: Es wird über den Competitive Ligand-Binding Assay (CLBA), einen Test zur Bestimmung von Thyroxin-bindendem Globulin (TBG) im Serum berichtet, der erstmals von Chopra et al. ((l 972), J. Clin. Endocrinol. Metab. 35,[565][566][567][568][569][570][571][572][573] beschrieben wurde. Die Bestimmung beruht auf der Verteilung einer konstanten Menge an markiertem Trijodthyronin (T 3 ) zwischen einer konstanten Menge an T 3 -Antikörpern und dem TBG des Serums, das zuvor durch Behandlung mit einem Anionenaustauscher (Amberlite IRA 400) von endogenem T 3 und T 4 freigemacht wurde. Der TBG-Gehalt von Normalpersonen beträgt 25,5 ± 5,0 mg/1 (x"± s x ); er ist signifikant erhöht bei Patienten mit Hypothyreose (36,8 ± 6,2 mg/1), bei Schwangeren (41,3 ± 6,4 mg/1) und signifikant erniedrigt bei Patienten mit Hyperthyreose (13,0 ± 4,0 rng/1). Kein Unterschied besteht zwischen Normalpersonen und Frauen, die Kontrazeptiva mit einem niedrigen Östrogenanteil einnehmen. Es besteht eine signifikante negative Korrelation zwischen TBG-Gehalt im Serum und dem relativen Anteil an freiem T 4 und freiem T 3 (r = -0,70, p < 0,001). Der niedrige TBG-Gehalt bei hyperthyreoten Patienten normalisiert sich allmählich unter thyreostatischer Therapie; die erhöhten TBG^Gehalte bei Hypothyreose fallen unter Substitutionstherapie in den Normbereich ab. Es zeigt sich eine Abhängigkeit der TBG-Konzentration vom Lebensalter. Mit zunehmendem Lebensalter kommt es zu einem signifikanten Abfall der TBG-Konzentration mit einem Minimum zwischen dem 20. und 50. Lebensjahr, danach erfolgt wieder ein signifikanter Anstieg auf die Ausgangswerte. Der CLBA-Assay ist eine einfache Routinemethode, die es ermöglicht, den TBG-Gehalt einer großen Anzahl an Serumproben genau und reproduzierbar zu messen. Der Vorteil gegenüber dem Radioimmunoassay für TBG liegt darin, daß eine Isolierung von TBG zur Antikörpergewin-nung und Markierung mit radioaktiven Isotopen, was zur Zeit noch mit erheblichen methodischen Schwierigkeiten verbunden ist, nicht erforderlich ist. Measurement of thyroxine binding globulin by competitive ttgand binding assay (CLBA)Summary: The competitive ligänd binding assay (CLBA) first described by Chopra et al. ((1972) J. Clin. Endocrinol. Metab. 35', 565-573) is a convenient routine method for the accurate measurement of thyroxine binding globulin in large numbers of serum samples. The assay is based on the partition of a constant quantity of radiolabelled T 3 between a fixed quantity of rabbit T 3 antibodies and the thyroxine binding globulin of the serum, after prior removal of T 3 and T 4 from the serum with an anion exchange resin (Amberlite IRA 400). In euthyroid subjects serum thyroxine binding globulin was 25.5 ± 5.0 mg/1, in hyperthyroid patients thyroxine binding globulin was significantly decreased to 13.0 ± 4.0 mg/1 and was significantly increased in hypothyroid patients to 36.8 ± 6.2 mg/1 as well as in pregnant women to 41.3 ± 6.2 mg/1. No difference was found between normal subjects and young women taking contraceptive puls wit...

In a 41-year-old woman and a 3-year-old girl, both of them with T3-thyrotoxicosis, serum levels of total and free T4 and T3 were measured serially during anti-thyroid drug treatment. Attempts to substitute thyroxine during the antithyroid treatment had to be interrupted because the patients became hyperthyroid again with excessive increases in total and free serum T3, even when concentrations of total and free T4 were brought to subnormal levels. The increased conversion of administered thyroxine ceased later on and higher amounts of oral T4 were tolerated after one year of treatment. In both patients there was an extremely low serum T4/T3 ratio, differing in this respect significantly from six other patients with T3-thyrotoxicosis and 41 patients with "conventional" T3/T4-hyperthyroidism. It is concluded that, in patients with T3-thyrotoxicosis due to excessive peripheral T4 to T3 conversion, substitution during antithyroid drug treatment should be either with very low doses of thyroxine or with triiodothyronine in divided daily doses. In such cases the level of serum T3 represents the most reliable biochemical measurement for the control of treatment, serum T4 levels being irrelevant.

No abstract