Association between use of FK506 and prevalence of post-transplantation diabetes mellitus in kidney transplant patients

BACKGROUND

Tacrolimus (FK506) use has been suggested as a risk factor for post-transplantation diabetes mellitus (PTDM) because it can impair insulin secretion. This association warrants further investigation. This study aimed to examine the prevalence of PTDM and its association with FK506 use in kidney transplant recipients. The study also aimed to examine the relationship of FK506 use and diabetes-related biologic markers.

METHODS

A retrospective chart review was used to collect data at a medical center in northern Taiwan from September 2003 to February 2012. PTDM was defined with the use of the criteria of the American Diabetes Association.

RESULTS

Among 166 patients included in the analysis, PTDM was reported in 49 patients (29.5%). A total of 93 patients used the FK506 regimen, of whom 34 (36.6%) were PTDM cases. Logistic regression showed that FK506 use (odds ratio [OR], 2.71; 95% confidence interval [CI], 1.20-6.11; P = .016) and older age (OR,1.08; 95% CI, 1.03-1.13; P = .001) were significant risk factors for PTDM. In addition, FK506 use in PTDM cases was associated with a significantly higher hemoglobin A1c level (7.55 vs 5.81; P = .01) and a borderline significantly higher insulin resistance index (3.24 vs 1.92; P = .053) than was FK506 use without the presence of PTDM.

CONCLUSIONS

Older age and an FK506 regimen were important predictors of the prevalence of PTDM. Greater early detection and prevention efforts for PTDM are needed for older transplant recipients. PTDM patients with an FK506 regimen had higher hemoglobin A1c levels and insulin resistance index than did patients who did not use FK506. The association of serum indicators with FK506 use in the prevalence of PTDM warrants further investigation.

LDL of Taiwanese vegetarians are less oxidizable than those of omnivores

The vegetarians in Taiwan consume diets high in polyunsaturated fatty acids. To investigate whether this dietary pattern results in high susceptibility of LDL to oxidation, 109 long-term (8 +/- 5 y) male and female vegans and lactovegetarians (ages 31-45 y) from Taipei and females from Hualien and matched omnivores were recruited to have 24-h-recall dietary assessments and blood lipid analysis. Body mass index and blood pressure were significantly lower in all vegetarian groups than in the matched omnivore groups (P < 0.05). Vegetarians consumed less energy except in the males and less protein, fat and cholesterol (P < 0.05). The mean polyunsaturated/saturated fatty acid (P/S) ratio of 2.4 in vegetarian diet was about two times that in omnivore diet (P < 0. 001). The concentrations of plasma total- and LDL-cholesterol (LDL-C) but not HDL-cholesterol (HDL-C) were significantly lower (P < 0.001) and resulting HDL-C/LDL-C ratio was 38, 46 and 30% higher (P < 0.01) in Taipei female, male and Hualien female vegetarians, respectively, than in the matched omnivores. Plasma triglyceride concentration was significantly lower only in the Hualien women vegetarians (31%, P < 0.001) than in the matched omnivores. The lag time of conjugated diene formation in LDL oxidized in vitro induced by copper was longer in Taipei female (62%, P < 0.001), male (29%, P < 0.05) and Hualien female (38%, P < 0.01), and the production of thiobarbituric acid reactive substances (TBARS) in LDL after 2-4 h of oxidation was 22-32% less (P < 0.005) in Taipei male and Hualien female vegetarians than the matched omnivores. Lag time of LDL oxidation was negatively related to LDL arachidonic (r = -0.55, P = 0.0003) and eicosapentaenoic (r = -0.47, P = 0.003) acid contents. LDL-TBARS production was negatively related to LDL linoleic acid content (r = -0.36, P = 0.023), but positively related to LDL arachidonic (r = 0.56, P = 0.0002) and eicosapentaenoic (r = 0.45, P = 0.004) acids. No significant differences were found in dietary vitamins C and E intakes and plasma LDL alpha-tocopherol concentrations between vegetarians and omnivores. Our results suggest that vegetarian diets decrease the susceptibility of LDL to oxidation despite their higher dietary P/S ratio.

Semiautomated typing of human papillomaviruses by restriction fragment length polymorphism analysis of fluorescence-labeled PCR fragments

A simplified version of a PCR-based reductional restriction fragment length polymorphism (rRFLP) approach for typing of human papillomaviruses (HPVs) is described previously [Wang et al., 1997]. It is achieved by the use of a biotin-labeled primer in PCR which, on restriction digestion and staining, is associated with only a single restriction fragment. In this report, we describe a further development of the rRFLP approach with the use of a fluorescence-labeled primer in PCR and fragment detection by laser scanning in an automatic sequencer. HPV typing is achieved by computer-assisted matching of the fluorescence-labeled rRFLP patterns with a database of rRFLP patterns of all known anogenital HPV types. On analysis of the typing of 133 HPV-positive cases using this procedure, 20 different HPV types were detected in exfoliated cervical cells in PAP smear samples derived from Taiwanese women. The results indicate the existence of a heterogeneous population of HPV types in Taiwan. Although most cases were associated with the more common HPV types, a significant fraction (about 20%) of the HPV types detected was related to the less common genotypes, which are often not included in commercial kits available for HPV typing. The results indicate the importance of covering as many HPV types as possible in clinical HPV genotyping protocols.

Lysosomal sulphate transport is dependent upon sulphydryl groups

Using thiol blocking agents, we examined the role of sulphydryl groups for function of the lysosomal sulphate transport system. Monothiol binding reagents, p-hydroxymercuribenzoic acid (p-HMB) and p-chloromercuribenzene sulphonic acid (p-CMBS), dithiol binding reagents such as CuCl2, the alkylating agent, N-ethylmaleimide (NEM), and NADH all inhibited lysosomal sulphate transport. The inhibitory effects of NEM and Cu2+ were not additive, suggesting that they both act upon the same critical sulphydryl group(s). Unlike the case for NEM, the inhibitory effects of Cu2+ were reversed by the reducing agent, dithiothreitol. Exposure to NEM resulted in a seven-fold increase in Km to 867 microM versus a control value of 126 microM and a modest decrease in Vmax to 99 pmolperunit beta-hexosaminidase per 30 s versus a control value of 129 pmolperunit beta-hexosaminidase per 30 s. Similar although somewhat less dramatic results were obtained using Cu2+ with an increase of Km to 448 microM and a Vmax of 77 pmolperunit beta-hexosaminidase per 30 s. The sulphate transport activity of detergent solubilized lysosomal membranes could be bound to a p-chloromercuribenzoic acid (p-CMB)-Sepharose sulphydryl affinity resin and eluted with mercaptoethanol. Sulphydryl groups thus appear to play a role in sulphate transport through effects on substrate affinity. Sulphydryl-binding appears to be a strategy that may be useful for purification of the transporter.

ATP stimulates lysosomal sulphate transport at neutral pH: evidence for phosphorylation of the lysosomal sulphate carrier

ATP markedly stimulated sulphate uptake by rat liver lysosomes that had been treated with N-ethylmaleimide to block the effects of the lysosomal proton-translocating ATPase (H+-ATPase). Maximal stimulation required millimolar concentrations of ATP and neutral buffer pH. ATP-stimulated transport exhibited saturation kinetics with a Km of 175 microM, identical with the Km for lysosomal sulphate uptake at pH 5.0, a process that does not require ATP. The requirement for ATP was specific: other nucleotides such as AMP, ADP, CTP, GTP, ITP and UTP failed to stimulate transport. Adenosine 5'-[beta,gamma-imido]triphosphate, the non-hydrolysable analogue of ATP, also failed to stimulate sulphate uptake, suggesting a requirement for ATP hydrolysis. Lysosomal pH, membrane potential and glucose transport were unchanged by the presence of ATP under the experimental conditions, consistent with a direct effect of ATP on the sulphate transporter. Exposure of lysosomes to protein kinase A and protein kinase C inhibitors did not alter the stimulation of sulphate transport by ATP. The lysosomal sulphate transport protein might be subject to regulation by a phosphorylation pathway that is not dependent on protein kinase A or protein kinase C.

Erratic oscillatory characteristics of plasma insulin concentrations in patients with insulinoma: mechanism for unpredictable hypoglycemia

Patients with insulin-producing tumors may have hypoglycemic symptoms at unpredictable times. This study evaluated whether plasma insulin oscillations, known to occur in normal individuals but not explored in patients with insulinomas, could be an underlying mechanism for such events. Nine normal subjects and five patients with proven insulinomas were studied in the fasting state. Serial sampling of arterialized blood over 80-100 min, at 2- or 3-min intervals was performed. In normal subjects, mean plasma glucose and insulin concentrations were 5.3 +/- 0.1 mmol/L and 58 +/- 9 pmol/L, respectively. Regular, low-amplitude plasma insulin oscillations were observed, with a period of 10-17 min. The subjects with insulinomas had lower mean plasma glucose and higher insulin concentrations than controls, 3.6 +/- 0.3 mmol/L (P = 0.01) and 150 +/- 42 pmol/L (P = 0.01), respectively. They also had insulin oscillations that appeared unstable as a result of variability in duration and amplitude compared with controls. The insulin pulses were irregular, and interpeak intervals varied between 4-54 min in different subjects; in some subjects, the amplitude was also variable, with sudden spontaneous pulses as high as 565 pmol/L, with an associated glucose decrement. We conclude that large spontaneous bursts of insulin secretion occur in patients with insulinomas as part of an erratic pattern of oscillatory insulin secretion, and these can account for unpredictable occurrences of hypoglycemia.

Reconstitution of lysosomal sulfate transport in proteoliposomes

As part of a strategy to purify the lysosomal sulfate transporter, we developed a method for reconstitution of transport in artificial membrane vesicles. Lysosomal membranes were prepared from Percoll density gradient purified rat liver lysosomes and membrane proteins were solubilized using the non-ionic detergent, Triton X-100. The solubilized proteins were mixed with liposomes prepared by sonication of egg yolk lecithin and the detergent was removed by passage of the mixture over Bio-beads XAD2. The resulting proteoliposomes exhibited saturable sulfate transport with characteristics that were very similar to those observed in lysosomal membranes. Transport in proteoliposomes had a Km of 155 microM, exhibited pH dependence and was sensitive to inhibition by DIDS. Reconstitution of transport in proteoliposomes may be useful as an assay for purification of the lysosomal sulfate carrier.

Lysosomal sulfate transport: inhibitor studies

Sulfate derived from the degradation of macromolecules is released from lysosomes via a carrier mediated process. In order to further characterize this process, recognized inhibitors of the erythrocyte band 3 anion transporter were examined for their effects on the lysosomal system. Studies with band 3 transport site inhibitors such as DIDS, SITS and phenylglyoxal indicated that, similar to the case for the band 3 protein, the lysosomal transporter has critical lysine and arginine residues. Band 3 translocation pathway or channel blocking inhibitors had mixed effects on the lysosomal system. 1,2-Cyclohexanedione, which covalently modifies a band 3 arginine residue distinct from that modified by phenylglyoxal, inhibited lysosomal sulfate transport. In contrast, the potent band 3 inhibitor dipyridamole had no effect on lysosomal sulfate transport indicating that there are some structural differences between the erythrocyte and lysosomal anion transporters. The band 3 translocation inhibitors niflumic acid and dinitrofluorobenzene were both effective inhibitors of the lysosomal system. Cupric ion inhibited sulfate transport while Ca2+, Co2+, Mg2+, Mn2+, and Zn2+ had no inhibitory effects. Exposure of intact lysosomes to trypsin largely ablated transport of sulfate. This information should be useful in efforts to further elucidate the structure and function of the lysosomal sulfate transporter.

Regulation of lysosomal sulfate transport by thyroid hormone

Sulfate transport was examined in rat liver lysosomes that were isolated from thyroid hormone-treated, thyroidectomized, and control animals. Sulfate uptake was significantly decreased in lysosomes from animals that had received intraperitoneal T3 (3,5,3'-triiodothyronine) at a dose of 20 micrograms/100 g body weight. The effect of T3 was maximal by 24 h post-injection and resulted in marked decreases in both Vmax (control: 155 +/- 33 pmol/unit of beta-hexosaminidase/30 s versus T3 treated: 24 +/- 7 pmol/unit of beta-hexosaminidase/30 s) and Km (control: 213 +/- 34 microM versus T3 treated: 92 +/- 6 microM). Thyroidectomy was associated with a significant increase in Vmax (control: 250 pmol/unit of beta-hexosaminidase/30 s versus thyroidectomized: 564 pmol/unit of beta-hexosaminidase/30 s), while Km was not significantly affected. The effect of thyroid hormone on lysosomal sulfate transport appeared to be relatively specific. In contrast to its effect on sulfate transport, T3 treatment had no effect on the uptake of either glucose or N-acetylglucosamine by rat liver lysosomes. Lysosomal pH, acidification in response to Mg/ATP, and the specific activities of alpha-L-iduronidase, beta-hexosaminidase, beta-D-glucosidase, and acid phosphatase were unaffected by T3 administration. Incubation of T3 with lysosomes from control animals had little or no effect on sulfate transport. Treatment of isolated lysosomes with either protein kinase A or alkaline phosphatase resulted in modest stimulation of transport. Thus, T3 does not appear to regulate transport by either direct interaction with the lysosomal transporter or protein kinase A-mediated phosphorylation. The exact mechanism for the inhibitory effect of T3 on lysosomal sulfate transport remains to be determined.

Evidence for pancreatic pacemaker for insulin oscillations in low-frequency range

Circulating insulin concentrations oscillate in regular fashion, with periods that fall into a high-frequency (period of 5-17 min) or low-frequency (period of 50-150 min) range. Only the high-frequency oscillations have so far been reported in vitro, suggesting that these derive from a primary pancreatic source. This study tested whether the low-frequency insulin oscillations could also be identified in vitro. Rat islets of Langerhans were perifused for 20 h using RPMI medium with 5.5 mM glucose. Perifusate fractions were collected at 9.9-min intervals. Mean insulin concentrations at the outset were 21.4 +/- 2.9 microU/ml, increased to 32.5 +/- 4.6 (P < 0.05) between 13 and 17 h after the start of perifusion, and then either leveled off or decreased to baseline. Superimposed on this general trend, we found sustained insulin oscillations with a period of 50-100 min. The mean amplitude was 14.2 +/- 4.2 microU/ml, and the amplitude/mean ratio was 64.6 +/- 12%. Spectral analysis revealed significant peaks at periods that were close to either 50 or 100 min and a smaller peak at 24-37 min. These data, using in vitro methodology and constant glucose concentrations, indicate the presence of sustained, spontaneous, low-frequency, ultradian insulin oscillations in the pancreatic islets. This provides evidence for a pancreatic component that may participate in the previously described in vivo ultradian insulin oscillations. This finding may also provide a mechanism for the apparent escape from glucose entrainment of serum insulin oscillations in non-insulin-dependent diabetes mellitus.

A mathematical model of oscillatory insulin secretion

Insulin is secreted in sustained oscillatory fashion from isolated islets of Langerhans. This finding has led to the assumption of an underlying synchronizing process that coordinates insulin oscillations. This assumption was tested by developing a mathematical model of oscillatory insulin secretion in which we included degree of synchrony as a parameter. We first evaluated insulin oscillations in perifused isolated rat islets, using spectral analysis to determine their regularity and frequency. A parsimonious mathematical model was developed to account for these characteristics. The model postulates a group of secretory units discharging at discrete intervals with the same underlying period. Variation from two sources, phase differences between units (synchrony) and regularity within units, is introduced by adding two normally distributed random variables with standard deviations (Sg and Si, respectively) to the secretory period. Sets of 100 simulations for different values of Sg and Si were run. Results of the simulations suggest that the system tolerates a relatively large degree of asynchrony yet still demonstrates regularity of oscillations on spectral analysis. Comparison with perifusion data suggests that a moderate degree of asynchrony between islets can best account for the pattern of insulin oscillations observed. This model provides a theoretical basis for the study of mechanisms for insulin oscillations.

Oscillations of lactate released from islets of Langerhans: evidence for oscillatory glycolysis in beta-cells

Oscillations in the glycolytic process have been demonstrated in a number of different biological systems. However, their presence has never been demonstrated in insulin-secreting beta-cells. We used lactate as a marker for glycolysis and measured lactate and insulin concentrations in the effluent of isolated perifused rat islets of Langerhans. Sustained regular oscillations in lactate concentrations with an average period of 16-20 min were observed in islets that were perifused with medium containing 5.5 or 16.7 mM glucose. Sustained oscillations of insulin concentrations secreted by the islets were also observed in these experiments, and the average period of oscillation was 14.6 +/- 2.3 min at 16.7 mM glucose. Mean insulin concentrations at 5.5 mM glucose were too low to permit analysis of oscillations. Spectral analysis confirmed the regularity of the lactate and insulin oscillations and showed peaks that were consistent with the average periods obtained using the Clifton program. Moreover, spectral analysis demonstrated marked similarity between the patterns of lactate and insulin oscillation during perifusion with 16.7 mM glucose. Cross-correlation analysis found these oscillations not to be consistently in phase. In conclusion, sustained oscillations in lactate released from islets of Langerhans suggest that the glycolytic process in beta-cells also oscillates. The similarity of the periods of lactate and insulin raises the possibility that oscillations in glycolysis may provide a mechanism for pulsatile insulin secretion.

Sustained pulsatile insulin secretion from adenomatous human beta-cells. Synchronous cycling of insulin, C-peptide, and proinsulin

The endocrine pancreas secretes insulin in a pulsatile fashion. This rhythm is generated at a site within the pancreas, although its precise location has not been determined. With an in vitro system, we tested the possibility that beta-cells might generate spontaneous pulsatile insulin secretion in the absence of any external influence. Human insulinoma tissue from five patients was perifused for 7-10 h with RPMI-1640 medium and constant concentrations of glucose (5.5 mM). Insulin, C-peptide, and proinsulin were measured in the effluent collected at 3.3-min intervals. All three peptides demonstrated pulsatility of secretion in a similar, synchronous fashion that was sustained throughout each study. The Clifton cycle detection program demonstrated cycling in all five tumors, with an average period for all tumors of 28, 29, and 26 min for insulin, C-peptide, and proinsulin, respectively. Spectral analysis confirmed the regularity and consistency of the hormonal secretory patterns. Mean hormone concentrations secreted by different tumors varied, but insulin and C-peptide were secreted in a nearly 1:1 ratio. This study demonstrates 1) that beta-cells are able to generate spontaneous pulsatile insulin secretory activity, which is independent of innervation or the presence of other islet cells, and 2) proinsulin secretion from the beta-cell also has an inherent pulsatility. The synchrony observed in the cycles of proinsulin and its peptide products confirms their common secretory pathway in the beta-cell. We conclude that the beta-cell may be the originator of insulin cycling.

Oscillations of circulating plasma insulin concentrations in the rat

In previous studies, we found that insulin is secreted in a pulsatile fashion in vitro in isolated rat pancreatic islets. This study evaluated whether similar plasma insulin fluctuations occur in the rat in vivo. Freely moving rats were implanted with a chronic jugular catheter and serial blood samples were obtained 48-72 hrs post surgery. Blood was sampled at 3 min intervals for 60 mins with volume replacement using a red cell preparation. Plasma insulin concentrations were observed to fluctuate around a mean of 10.6 +/- 1.1 uU/ml, with an amplitude of 4.7 +/- 0.5 uU/ml and a period of 13.3 +/- 1 mins (n = 6). This was similar to the cycling observed in isolated islets at similar glucose concentrations. Sampling during the dark phase of the light-dark cycle in the rat was associated with an increase in the mean plasma level, amplitude and period of insulin oscillations compared with values obtained during the light phase (n = 3). These data are the first in vivo demonstration of oscillatory circulating insulin concentrations in the rat and show that the pulsatility in this species is similar to that observed in other mammals including man. We conclude that the chronically catheterised rat is a useful model for the evaluation of oscillating insulin concentrations in vivo, and may provide interesting insights by comparison with in vitro data in the same species.

Analysis of the unoccupied site of an integrated human papillomavirus 16 sequence in a cervical carcinoma

We have previously cloned and analyzed the structure of a type 16 human papillomavirus (HPV16) integration in a primary cervical carcinoma tissue, M50 (Choo et al., J. Virol. 62, 1659-1666, 1988). We found that specific nucleotide sequences within the HPV16 genome influenced the genomic organization of the integrated viral genome. Using the viral-cellular junctions of the M50 DNA as probes, we have now cloned the unoccupied site from a human genomic library. Mapping analysis showed that a deletion of about 1.1 kilobase pairs (kb) had occurred at the integration site of M50. Sequencing of the integration junctions of the unoccupied site and comparison with the viral sequence has revealed short regions of sequence homology between the viral and the cellular genomes at both junctions. Our results are consistent with a mechanism of integration of the HPV16 sequences in the M50 carcinoma involving illegitimate recombination events using short patches of homologous sequences between the two heterologous genomes for anchorage and as guides for crossover. Preferred topoisomerase I cleavage sites and alternating purine and pyrimidine bases, which favor the formation of Z-DNA, could also be identified at the integration regions, supporting a proposed role for the topoisomerase I enzyme in the illegitimate recombination in the viral integration process.

Pulsatile insulin secretion in isolated rat islets

The pancreas secretes insulin in an oscillatory fashion, but the precise site of the pacemaker for pulsatile insulin secretion has not been identified. These studies were designed to determine whether islets also secrete insulin in a pulsatile fashion if they are isolated from their pancreatic milieu. Isolated rat islets (80-100) were perifused 8 h in culture medium after overnight incubation, and samples were collected at 3.3-min intervals. Insulin secretion was evaluated for pulsatility with the Clifton Cycle Detection Program. Perifusion of islets was associated with a spontaneous, persistent, and regular pulsatility of insulin secretion, which was observed in all conditions tested. Perifusion with medium containing 5.5 mM glucose (n = 11) demonstrated oscillations with a mean periodicity of 17.6 +/- 1.1 min and a mean amplitude of 4.8 +/- 0.4 microU/ml when overall mean insulin concentration was 16.7 +/- 2.4 microU/ml. When the glucose concentration was 16.7 mM (n = 9), overall mean insulin concentration was 54.4 +/- 2.6 microU/ml, with increases in periodicity (22.0 +/- 1.3 min) and amplitude (10.7 +/- 0.5 microU/ml). All measurements were significantly different from those observed during perifusion with 5.5 mM glucose (P less than 0.02-0.001). Theophylline (1 mM) also enhanced the overall mean insulin concentration and amplitude (69.4 +/- 10.4 and 14.2 +/- 1.2 microU/ml, respectively) compared with control studies without theophylline (16.7 +/- 5.3 and 4.3 +/- 0.5 microU/ml) (P less than 0.01). The period of the cycle was also increased from 17.5 +/- 1.1 to 26.4 +/- 6.3 min, but this was not significantly different from the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the structure and expression of the c-myc oncogene in cervical tumor and in cervical tumor-derived cell lines

The structure of the c-myc oncogene in 17 cervical tumors and patient-matched nontumor tissues from Chinese patients residing in Taiwan was analysed. In contrast to recent reports on Mexican patients, none of the samples showed rearrangements and sequence amplification in the c-myc gene. The discrepancy may be explained by different carcinogenesis mechanisms being in operation in different geographic regions. Although no structural alterations in the c-myc gene were found in seven cervical carcinoma cell lines analysed, Northern blot analysis indicated different levels of c-myc gene expression which may be related to the presence of human papillomavirus (HPV) sequence in the cell and suggests a possible c-myc-hpv interaction in some stages of the transformation process.

Effect of gangliosides on primary and secondary plaque-forming cells responses and on suppressor T-cells induction

This study was designed to determine the suppressive effect of bovine brain gangliosides on primary and secondary anti-sheep red blood cell (SRBC) plaque-forming cells (PFC) response. Spleen cells from inbred C57BL/6J mice were used as sources of lymphocytes. The result showed that levels of gangliosides at 50 and 100 micrograms/ml suppressed primary anti-SRBC PFC responses about 30% and 60%, respectively, of normal control. In contrast, secondary anti-SRBC PFC were not suppressed by the same levels of gangliosides. Likewise, PFC response from mixing SRBC-primed T-cells with naive B-cells was not suppressed by gangliosides. In addition, induction of suppressor T-cells was reduced by 50 and 100 micrograms/ml of gangliosides, 57% and 63%, respectively, versus 86% of suppression of PFC response by the control suppressor T-cells. These results further suggest the role of gangliosides as immunomodulators.

Influence of age, strain, and beta-adrenergic agonist on insulin sensitivity in chicks as determined by an adaptation of the euglycemic clamp technique

The euglycemic clamp technique has been widely used to examine changes in in vivo insulin sensitivity during physiological changes in mammals. The technique offers the advantage that the tissue uptake of glucose induced by a set dose of insulin is determined at the normal (steady state) circulating concentration of glucose (euglycemia). The euglycemic clamp technique has been modified to examine in vivo sensitivity to insulin in chickens. Insulin sensitivity is determined by the rate of infusion of exogenous glucose required to maintain euglycemia. Young (6 to 8-wk-old) male chickens (White Leghorn) are more sensitive to insulin than adult males of the same strain. There is, however, no difference in insulin sensitivity between young male chicks of broiler and White Leghorn strains. Chronic administration of beta-adrenergic agonist (L-640,033, donated by Merck, Sharp, and Dohme Research Laboratories, Rahway, NJ) in the diet, at levels of 0, .25, 1.0, and 4.0 ppm for 3 to 5 days also did not influence in vivo insulin sensitivity.

Luteinizing hormone secretion from anterior pituitary cells of the cockerel: evidence for an ultradian rhythm

Studies were conducted to characterize the secretory pattern of luteinizing hormone (LH) from perfused anterior pituitary cells of the cockerel in the presence and absence of secretagogues. Basal LH secretion was found to occur in a rhythmic pattern, with the mean cycle period for 5 different perfusion columns estimated to be 66.4 +/- 4.0 min. By contrast, when cells were repeatedly exposed to luteinizing hormone-releasing hormone (LHRH) at 90-min intervals, the period of the LH rhythm was altered to approximate the interval of LHRH pulses (96.7 +/- 6.1 min; n = 3 perfusion columns). Exposure of cells to media containing 50 mM potassium chloride (KCl) augmented the release of LH and slightly decreased the cycle period compared to that which occurs during basal secretion (49.2 min) but did not eliminate the rhythm. Finally, perifusion of cells with medium containing 10 microM colchicine eliminated the rhythm of secretion. These data suggest that there exists an ultradian rhythm of LH secretion from the chicken pituitary which is expressed in the absence of hypothalamic input and is modified by the hypothalamic releasing factor, LHRH. In addition, the rhythm does not seem to be affected in the short-term by a small depolarization of the membrane as occurs with the addition of KCl to the perifusion media but does seem to be dependent upon microtubule function.

Luteinizing hormone releasing activity of [Gln8]-LHRH and [His5, Trp7, Tyr8]-LHRH in the cockerel, in vivo and in vitro

The luteinizing hormone (LH)-releasing activity of two distinct chicken luteinizing hormone releasing hormones ([Gln8]-LHRH and [His5, Trp7, Tyr8]-LHRH) were evaluated in white Leghorn cockerels. In the first study, thirty birds were randomly allotted to five groups and injected, i.v., with 0.9% saline, [Gln8]-LHRH (cLHRH I, 1 microM or 10 microM) or [His5, Trp7, Tyr8]-LHRH, (cLHRH II; 1 microM or 10 microM). Blood samples were drawn prior to and through 60 min following the injection, and plasma was collected for LH determination. In the second study, anterior pituitary cells from cockerels were dispersed and preincubated for 1 hr. Approximately 1.5 X 10(5) cells per tube were incubated with either Medium 199 buffer (control), 8-bromo-cAMP or various doses of cLHRH I or cLHRH II at final concentrations ranging from 0.02 to 100.0 nM. At the end of a two hour incubation, supernatant was collected and the concentration of LH determined. Injection of cLHRH I or cLHRH II at 1 microM and 10 microM levels caused a significant increase in blood LH concentrations which peaked 5 min following injection. There were, however, no differences between the stimulatory effect of cLHRH I compared to cLHRH II at either dose. On the other hand, cLHRH II was found to be 4.7 times more potent than cLHRH I in stimulating LH release from dispersed pituitary cells. It is suggested that cLHRH II may have greater affinity for the gonadotroph receptor, greater uptake by the cell, and/or that it may be more resistant to in vitro degradation than cLHRH I. On the other hand, an extra pituitary site of degradation may be more effective in metabolizing cLHRH II, resulting in its equipotency with cLHRH I, in vivo.

Intestinal calcium absorption and bone morphology in magnesium deficient chicks

Calcium absorption was measured by 47Ca disappearance from ligated duodenal loops and 47Ca uptake by tibiae in chicks fed diets containing one of four levels of Mg for two weeks. The diets, otherwise identical, contained 88 (group 1), 150 (group 2), 200 (group 3) and 1000 (group 4) ppm Mg. There were no statistically significant differences in 47Ca absorption. Mucosal CaBP and intestinal alkaline phosphatase were slightly, but not significantly, elevated in the Mg depleted chicks in groups 1 and 2 compared to groups 3 and 4. Microscopic examination of the tibiae showed marked alterations in morphology in chicks fed the 88 ppm Mg diet. The thickness of the epiphyseal plate was reduced, and the morphologic signs of osteolysis and chondrolysis, normally observed in the metaphysis, appeared to be absent. The mid-diaphysis was thickened and showed marked reduction in both osteoblast and osteocytie activity. Blood calcium levels were significantly reduced in the Mg deficient chicks. It was concluded that Mg depletion in chicks altered Ca homeostasis primarily by changing bone structure and function.