1. The uptake of gamma-aminobutyric acid (GABA) into rat thyroid slices was studied. 2. Uptake of 14C-GABA was concentration-dependent: one unsaturable (diffusion) and two saturable components obeying Michaelis-Menten kinetics contributed to transport. 3. The kinetic constants of saturable GABA transport systems were: Km1 = 1.5 microM, V1 = 4.0 nmol x (g wet weight)-1 x (20 min)-1 (high-affinity uptake): Km2 = 800 microM, V2 = 260 nmol x (g wet weight)-1 x (20 min)-1 (low-affinity uptake). 4. Uptake mediated by each of the carrier systems was concentrative, entirely Na+-dependent, and required activation energies characteristic for active transport. 5. High-affinity transport was structurally specific for GABA. The substrate specificity of low-affinity uptake resembled that of beta-amino acid transport systems.
The uptake of gamma-aminobutyric acid (GABA) in the thyroid gland of the rat was studied autoradiographically following in vitro incubation. High-affinity GABA uptake was localized in follicle cells, whereas C cells (parafollicular cells) in general did not accumulate GABA by high-affinity transport. The follicle cells were also the main sites of low-affinity GABA uptake. Additionally, some nerve fibres were found to accumulate GABA. The predominant localization of GABA uptake in follicle cells is discussed in view of a presumed role of GABA in thyroid function.
To examine whether lysosomal enzymes play a part in the involution of corpora lutea, cathepsin D was assayed in both the lysosomal fraction ('bound' cathepsin D) and the postlysosomal supernatant fluid ('free' enzyme), by measuring the increment in absorbance at 280 nm caused by acid-soluble material released from haemoglobin. From these data the release ratio (free : bound specific activity) was calculated. In corpora lutea on days 5 and 15 of pregnancy, the values for lysosome-bound specific activity (units of E280/h/mg protein) were 4\m=.\76\ m=+-\ 0\m=.\51and 5\m=.\00\ m=+-\ 0\m=.\29 (s.e.m.), and the release ratios were 0\m=.\12\ m=+-\ 0\m=.\02and 0\m=.\11 \m=+-\ 0\m=.\01 respectively. Similar values were obtained in newly formed corpora lutea of dioestrous and pro-oestrous rats, but on the day of oestrus the level of cathepsin D bound to lysosomes decreased to 2\m=.\66\ m=+-\ 0\m=.\36and the release ratio increased to 0\m=.\36\m=+-\ 0 \ m= . \ 0 3 . On day 5 of prolactin-induced pseudopregnancy, the activities of cathepsin D in both cellular fractions resembled those of pregnancy. An even higher level of lysosome-bound cathepsin D ( 7\ m=. \ 11 \ m=+-\ 0\m=.\47) with a relatively low level of free activity (release ratio 0\m=.\18\ m=+-\ 0\m=.\02) was observed in lactating rats (day 7 of lactation), in the persistent corpora lutea of pregnancy. Administration of prostaglandin F2\g=a\(PGF2\g=a\) on days 4, 5 and 6 of lactation significantly decreased the level of lysosome-bound cathepsin D measured on day 7 in the persistent corpora lutea of pregnancy (3\ m=. \ 81 \ m=+-\ 0\m=.\24) and increased the release ratio (0\m=.\40 \ m=+-\ 0\m=.\05). The intracellular distribution of acid phosphatase did not show a consistent relationship with the reproductive state. It appears that a decrease in the amount of lysosome-bound cathepsin D is associated with incipient luteolysis, that prolactin inhibits release of cathepsin D from the lysosomes and that PGF2\g=a\ counteracts this action of prolactin.
The effect of extracorporeal photopheresis (EP) on various cytogenetic parameters has been investigated. During EP the photoactivatable agent 8-methoxypsoralen (8-MOP) was administered orally. After 2 h a leukocyte-enriched blood fraction was collected by haemocentrifugation, irradiated with UVA extracorporeally, and reinfused to the patient. Two patients suffering from cutaneous T-cell lymphoma showed a marked clinical improvement in response to therapy. In order to investigate the cytogenetic effects and mutagenic risk of EP, the mitotic index (MI), the type and number of chromosomal aberrations and the rate of sister chromatid exchanges (SCE) were studied. Following EP treatment the patients' lymphocytes were cultured and stimulated with phytohaemagglutinin (PHA) for 48 or 72 h. The cultured lymphocytes showed a decreased MI after 48 h as an indicator of cytotoxic effects, but not after 72 h. In lymphocyte cultures not stimulated with PHA, the MI was decreased even after 72 h. The number of chromosomal aberrations and SCE were increased upon treatment, but only transiently, returning to basal levels between consecutive treatments. Our data provides no evidence for increased mutagenic risk as a consequence of effective EP treatment.
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