Contraction-related factors affect the concentration of a kallidin-like peptide in rat muscle tissue

Abstract

In order to study the effects of the manipulation of various factors related to muscular activity on the concentration of kinins in muscular tissue, a microdialysis probe was implanted in the adductor muscle of the hindlimb in anaesthetized rats. After collection of baseline samples, the perfusion fluid was changed to a Ringer solution containing sodium lactate (10 or 20 mM), adenosine (50 or 100 microM) or a lower pH (7.0 or 6.6). Whereas perfusion with lactate did not have any significant effect on the concentration of kinins in the dialysate, the perfusion with a lower pH or with adenosine dose-dependently increased the kinin content in the samples. In a second microdialysis experiment, by using specific radioimmunoassays (RIA) for bradykinin and kallidin, we observed that about 70 % of the total kinins dialysed from rat muscle are a kallidin-like peptide. Also, the simultaneous perfusion with 100 microM caffeine totally abolished the increase in kinin levels induced by the perfusion at pH 6.6. In a third experiment, soleus muscles from rat were stimulated in vitro during 30 min in the presence or absence of 77 microM caffeine. Electrically stimulated contraction, but not the addition of 10 mU ml(-1) insulin, induced an increase in the concentration of the kallidin-like peptide in the buffer. This effect was totally prevented by the addition of the adenosine antagonist caffeine. These results show that a kallidin-like peptide is released from rat muscle, and that its production is enhanced by muscle activity. Furthermore, the increase in kinin peptides during muscle contraction may be mediated by an increase in adenosine levels.

Figure 1. Kinin levels after insertion of a microdialysis probe in adductor muscle

Changes (expressed as percentage of the mean concentration of the first baseline sample, mean ±s.e.m.) in the microdialysis concentration of kinin peptides (A; measured as bradykinin, n= 7), kallidin (B; n= 4) and bradykinin (C; n= 4) from the implantation of the microdialysis probe to the start of baseline sampling.

Figure 2. Effect of pH, adenosine and lactate on muscle kinin levels

Changes (expressed as percentage of the mean concentration of the three baseline samples) in the microdialysis concentration of kinin peptides (measured as bradykinin), after perfusion with Ringer solution (control •, n= 5), Ringer solution containing 10 and 20 mm lactate (lactate ▿, n= 6), Ringer solution at pH 7.0 and 6.6 (pH ▪, n= 6), or Ringer solution containing 50 and 100 μM adenosine (adenosine ⋄, n= 7).

Figure 3. Effect of dihydralazine on muscular kinin liberation induced by adenosine

Changes (expressed as percentage of the mean concentration of the three baseline samples) in the microdialysis concentration of kinin peptides (measured as bradykinin) after the perfusion with Ringer solution (control •, n= 5), or 50 and 100 μM adenosine in Ringer solution (adenosine ▿, n= 7) or in Ringer solution containing 125 mg l⁻¹ dihydralazine (adenosine + DHZ ▪, n= 5).

Figure 4. Effect of caffeine on the increase on muscle kinin levels induced by low pH

Changes (expressed as percentage of the mean concentration of the three baseline samples) in the microdialysis concentration of kallidin (A) and bradykinin (B) after the perfusion with Ringer-acetate solution at pH 6.6 (•; n= 5) or Ringer-acetate solution at pH 6.6 containing 100 μM caffeine (○; n= 6).

Figure 5. Effect of caffeine on kallidin levels after muscle stimulation in vitro

Levels of kallidin (expressed as pm) in the incubation medium of rat soleus muscle after 30 min rest (C), electrical stimulation during 30 min (S), addition of 10 mU ml⁻¹ insulin (I), or electrical stimulation during 30 min with the addition of 10 mU ml⁻¹ insulin (S + I), with (open columns) or without (filled columns) the addition of 77 μM caffeine (n= 12 for each treatment). *P < 0.05 vs. control without caffeine (2 sided Dunnett's test).