Ying-I Peng

Recovery of high potassium-evoked dopamine release after depolarization challenge in the striatum of young and old male rats.

The aim of this study was to assess the recovery of high potassium-evoked dopamine (DA) release after depolarization challenge in young (3-4 months) and old (21-25 months) male Wistar rats. Recovery of DA release was evaluated by comparison of the peak responses of DA release induced by two serial high potassium stimulations. Concentric microdialysis probes were stereotaxically implanted in the lateral striatum of rats, and microdialysis was commenced 24 h after surgery. Using a low flow rate of perfusion (1 microl/min), all rats received 2 x 20 min infusions of 100 mM potassium solution separated by either 60 or 140 min. No difference in the basal DA concentration or the potassium-evoked DA release or its recovery was seen between the two groups. Our results suggest that the vesicular DA store recovers rapidly after high potassium challenge in both young and old rats.

Aminoguanidine prevents age‐related aortic stiffening in Fisher 344 rats: aortic impedance analysis

We determined the effects of long‐term treatment with aminoguanidine (AG), an inhibitor of advanced glycation end products, on the mechanical properties of the arterial system in aged Fisher 344 rats, using the aortic impedance analysis. Normotensive rats were treated from 18 to 24 months with AG (1 g/l−1 in drinking water) and compared with a control group. Pulsatile aortic pressure and flow signals were measured and then subjected to Fourier transformation for the analysis of aortic input impedance. Wave transit time was determined using the impulse response function of the filtered aortic input impedance spectra. With no alteration in body weight, rats treated with AG had decreased heart weight compared with the aged untreated controls. AG did not affect arterial blood pressure; however, the age‐related increase in total peripheral resistance was prevented by AG. AG retarded the age‐related decline in aortic distensibility, as evidenced by a reduction of 25.2% in aortic characteristic impedance and an increase of 28.1% in wave transit time. Meanwhile, the increase in wave reflection factor in aging rats was reduced by 32.3% by AG. Both the increased wave transit time and the decreased wave reflection factor suggest that AG may prevent the age‐related augmentation in systolic loading condition for the left ventricle coupled to the arterial system. We conclude that long‐term treatment with AG may impart significant protection against aortic stiffening and cardiac hypertrophy in aged Fisher 344 rats.

Hypotensive effects of captopril on physical properties of the arterial system in young and adult rats

We determined the acute effects of the angiotension converting enzyme inhibitor captopril on the arterial mechanics in rats at different ages, based on the exponentially tapered T-tube model. Male Wistar-Kyoto rats aged 4 and 12 months were individually referred to as young (n = 8) and adult rats (n = 8) and wereanesthetized and thoractomized. The pulsatile aortic pressure andflow signals before and after the administration of captopril (20mg/kg, i.p.) were measured by a high-fidelity pressure sensor andan electromagnetic flow probe, respectively. In each age group,captopril showed little change in basal heart rate as well ascardiac output. However, captopril produced a drop of 15% in meanaortic pressure in young and a fall of 12% in adult rats. Inaddition, captopril reduced total peripheral resistance by 21% inyoung and by 23% in adult animals. As for the pulsatile nature ofthe arterial system, captopril had increased wave transit time ofthe lower body circulation of 10% in young and of 12% in adultrats. By contrast, captopril reduced wave reflection factor by22% in young and by 25% in adult animals. In conclusion, theconverting enzyme inhibitor captopril has a stiffness-decreasingeffect on Windkessel vessels and a dilated effect on resistancearterioles in either young or adult rats. No age dependence ofvascular response and reflex tachycardia to captopril has beenfound in rats between 4 and 12 months.

Evaluation of L-DOPA biotransformation during repeated L-DOPA infusion into the striatum in freely-moving young and old rats.

The aim of this study was to assess changes in L-3, 4-dihydroxyphenylalanine (L-DOPA) biotransformation in response to two-pulse infusion of L-DOPA into the striatum of freely-moving young (3-4 month) and old (21-26 month) male Wistar rats. In addition, the effects of L-DOPA infusion on the vesicular dopamine (DA) store in young rats were also studied. Both L-DOPA-induced DA overflow and uptake of the perfused L-DOPA by the striatum were used to study L-DOPA biotransformation during microdialysis. High potassium-induced DA depletion was performed to assess the dynamics of the vesicular DA store following L-DOPA infusion. Concentric microdialysis probes were stereotaxically implanted in the lateral striatum of rats of both age groups and microdialysis was begun 24 h later. All rats received 2x20 min infusions of 3 mgr L-DOPA separated by an interval of 60 min. In the striatum of both groups, L-DOPA-induced DA overflow and uptake of exogenous L-DOPA were both significantly enhanced during the second infusion compared to the first. In young rats, when a 20-min infusion of 3 mgr L-DOPA was given between 2x20 min infusions of 100 mM potassium, no increased DA release was seen at the second high potassium challenge compared with the first. Our results suggest that the enhancement of DA overflow induced by the second L-DOPA infusion is, at least partially, due to an increase in L-DOPA biotransformation, and not simply to an enlarged DA pool. In contrast to the in vitro results, our own in vivo results show that L-DOPA utilization in the aging striatum does not deteriorate with age.