T-1032, a cyclic GMP phosphodiesterase-5 inhibitor, acutely blocks physiologic insulin-mediated muscle haemodynamic effects and glucose uptake in vivo

Abstract

1. Cyclic GMP phosphodiesterase-5 inhibitors have been shown to alter blood flow in specific tissues by potentiating local NO-dependent vasodilatory mechanisms. Since the haemodynamic effects of physiologic insulin, particularly capillary recruitment, may be critical for muscle glucose uptake in vivo and are blocked by inhibitors of nitric oxide synthase, we have explored the acute effects of the specific cGMP phosphodiesterase-5 inhibitor T-1032 on physiologic insulin action in anaesthetized healthy rats in vivo. 2. Whole-body glucose infusion (GIR), femoral blood flow (FBF), hind leg vascular resistance (VR), hind leg glucose uptake (HGU), 2-deoxyglucose uptake into muscles of the lower leg (R'g), hind leg metabolism of infused 1-methylxanthine (1-MX), a measure of capillary recruitment, and muscle cGMP were determined. The experimental groups were T-1032 (10 microg min-1 kg-1) infused for 1 h before and during a euglycaemic insulin clamp (3 mU min-1 kg-1 x 2 h), T-1032 infused for 3 h with saline, T-1032 during a 2 h clamp, T-1032 with saline for 2 h, and a 2 h saline control. 3. Insulin increased GIR from zero to 13 mg min-1 kg-1, HGU from 0.1+/-0.01 to 0.43+/-0.05 micromol min-1, R'g and 1-MX, marginally increased FBF, and had no effect on blood pressure or heart rate. T-1032 alone had no effect on blood pressure, heart rate, FBF, VR, HGU, R'g or 1-MX, but increased muscle cGMP. T-1032 1 h before and during insulin completely blocked GIR (1 h), HGU (2 h), R'g (2 h), and 1-MX (2 h). T-1032 commenced with insulin had only partial blocking activity against insulin. 4. We conclude that T-1032 is a potent acutely acting inhibitor of the muscle effects of physiologic insulin on capillary recruitment and glucose uptake in vivo. These, together with inhibition of whole-body glucose infusion during insulin, may caution against the use of isoenzyme-5-specific cyclic GMP phosphodiesterase inhibitors as therapeutic agents.

Figure 1

Study design. The protocol involved the euglycaemic clamp at 3 mU min⁻¹ kg⁻¹ insulin, commencing at time=0 min, and either saline or T-1032, which was commenced at time=−60 min, or jointly with insulin. Duplicate arterial and femoral venous plasma samples were collected at 120 min, for HPLC analysis, plasma glucose, T-1032, and insulin determinations. Venous infusions are indicated by the bars. Bolus injections of allopurinol or 2-DG were made as indicated. The arterial samples were taken for glucose determinations as indicated. Venous infusions are indicated by the bars. Muscle samples were taken at 120 min for 2-DG and cGMP analyses.

Figure 2

Cardiovascular changes elicited by infusion of insulin, T-1032, and combinations of the two. Time courses from the protocol of Figure 1 are shown for mean arterial blood pressure (BP), heart rate (HR), and changes in FBF and VR. The values are means±s.e. *Significantly different (P<0.05) from saline infusion, and #significantly different (P<0.05) from insulin+T-1032.

Figure 3

Glucose infusion rate (GIR) for clamps at 3 mU min⁻¹ kg⁻¹ insulin with and without T-1032. Data were collected from samples taken, as shown in the protocol of Figure 1. Values are means±s.e. *Significantly different (P<0.05) from insulin infusion.

Figure 4

HGU and [³H]2-DG uptake (R′g) values for combined and individual muscles for clamps at 3 mU min⁻¹ kg⁻¹ insulin with and without T-1032, using the protocol of Figure 1 and determined at 120 min. Individual R′g for soleus, plantaris, gastrocnemius red, gastrocnemius white, EDL, and tibialis at 120 min have been combined. The values shown are means±s.e. *Significantly different (P<0.05) from saline infusion, and #significantly different (P<0.05) from insulin.

Figure 5

Hind leg 1-MX metabolism for clamps at 3 mU min⁻¹ kg⁻¹ insulin with and without T-1032 using the protocol of Figure 1 and determined at 120 min. The values shown are means±s.e. *Significantly different (P<0.05) from saline infusion, and #significantly different (P<0.05) from insulin.