Design of temperature-responsive polymers with enhanced hysteresis: alpha,alpha-disubstituted vinyl polymers.

Three temperature-responsive polymers which are alpha,alpha-disubstituted vinyl polymers having two amphiphilic groups (ethylamide or ethylester) per monomeric unit were designed. Two of these polymers showed unusually large hysteresis in their phase transition temperatures between a heating and a cooling process. This hysteresis resulted from the extremely slow kinetics of the dissolution process of the aggregated polymer chains in the cooling process due to intra- and interchain interactions including hydrogen bonding and hydrophobic interaction. The high density of the amphiphilic substituents on the polymer chain due to the alpha,alpha-disubstituted structure enhanced these intra- and interchain interactions. The large hysteresis was also observed in the volume change of a corresponding hydrogel. These new classes of temperature-responsive polymers are interesting materials because their large hystereses can be regarded as erasable memory function.

Central and peripheral administration of amylin induces energy expenditure in anesthetized rats.

Amylin is a peptide hormone that is co-released with insulin from pancreatic beta-cells following a meal. Intracerebroventricular (icv) administration of amylin (1-100 pmol), or an amylin agonist, salmon calcitonin, elicited dose-dependent thermogenic, tachycardic, and hyperthermic responses in urethane-anesthetized rats. Intravenous (iv) administration of higher doses of amylin (100 pmol-20 nmol) also induced similar responses, although the amplitudes of these responses were significantly smaller than those elicited by icv administration, suggesting the primary action of amylin to be in the brain. However, the iv administration of amylin induced the responses slightly faster than the icv injection, the former responses occurring<4 min and the latter, at 8-10 min, after the administration. The iv but not the icv injection of amylin increased the respiratory exchange ratio transiently (<20 min), though the thermogenic response lasted for a longer period after both injections, indicating a shift from mixed fuel to predominantly carbohydrate utilization in the initial phase of thermogenesis induced by the iv injection of amylin. The differences in substrate utilization and latency of the responses suggest that the actions of amylin include partly different targets when administered centrally and peripherally. Moreover, pretreatment with a beta-adrenergic blocker, propranolol (5 mg kg(-1), iv), blocked all responses elicited by either icv or iv administration of amylin, whereas ablation of the area postrema in the hindbrain did not influence the effects of icv-administered amylin. These results suggest the involvement of amylin in postprandial energy expenditure, mediated by peripheral beta-adrenoceptors.